Your FREE ASE T8 Preventive Maintenance Inspection (PMI) Practice Test 2026 – 180+ Q&A

Correct answer: Worn piston rings

Worn piston rings let crankcase oil slip past into the combustion chamber, where it burns and leaves heavy blue smoke at the stack. Low fuel pressure and a weak fuel lift pump starve the injectors, which costs power but leans the mixture rather than producing smoke. A low coolant level leads to overheating and a temperature warning, but on its own it does not put oil or extra fuel into the cylinder, so it does not explain the smoke.

Correct answer: Removing harmful blowby vapors

The PCV system works by removing harmful blowby vapors from the crankcase and routing them to the intake so they are burned instead of vented, which also keeps crankcase pressure from building. Injected fuel volume is metered by the injectors under control-module command; exhaust oxygen content is read by the oxygen sensor; intake boost pressure is limited by the wastegate.

Correct answer: Lowering nitrogen oxide emissions

Feeding a measured share of inert exhaust back into the intake dilutes the charge and drops peak combustion temperature, and lowering nitrogen oxide emissions is the result the system exists to produce. Turbocharger shaft speed is set by the wastegate or variable-geometry actuator; cylinder coolant passages are warmed by the cooling circuit and thermostat; pilot injection quantity is metered by the injectors.

Correct answer: Exhaust gas turbocharger

The exhaust gas turbocharger uses exhaust energy to spin a compressor wheel that packs a denser air charge into the cylinders, which is the compression work asked about here. A camshaft position sensor only reports shaft angle to the control module; a service brake compressor charges the vehicle air tanks and is not part of the intake path; a crankshaft damper pulley absorbs torsional vibration and drives accessories.

Correct answer: Coolant has reached a warm sump and emulsified the oil

A light tan, frothy, milky dipstick sample means coolant has reached a warm sump and emulsified the oil, pointing to a head gasket, cracked head or oil cooler leak. Water that has condensed in a cold crankcase leaves a film under the fill cap, not a milky sample throughout. Air whipped past the windage tray from an overfilled sump makes amber foam that settles. Fuel that has leaked past the injectors and thinned the oil keeps the oil dark.

Correct answer: A short wait after shutdown with flat ground

The accurate method is a short wait after shutdown with flat ground under the truck, so oil drains back from the galleries and head into the pan and the dipstick sits level. Just after shutdown, much of the hot oil is still up in the engine, so the level reads low. Checking while idling hot in neutral, even on a level floor, is the procedure for an automatic transmission, not engine oil. After a cold overnight soak the oil has drained back, but a nose-up park tilts the pan and skews the reading.

Correct answer: Hand refractometer

A hand refractometer reads the bend of light through a drop of coolant, so it reports freeze protection accurately and is largely unaffected by sample temperature. A coolant hydrometer floats balls in the fluid and is sensitive to temperature, which is why the hydrometer method was withdrawn in favor of a refractometer method. An infrared pyrometer measures surface temperature and a digital multimeter measures electrical values; neither reports glycol concentration.

Correct answer: A 50/50 blend of glycol and clean soft water

A 50/50 blend of glycol and clean soft water is the balanced mixture: it protects to roughly -34 degrees F, raises the boil point, and keeps the additive package working. A 70/30 blend of glycol and boiled tap water is too rich, so it carries heat poorly and freeze protection actually falls off. A 50/50 blend of glycol and boiled tap water has the right ratio, but boiling removes only temporary hardness, leaving the chlorides, sulfates and other dissolved minerals that cause scale and corrosion. A 50/50 blend of glycol and plain well water also has the right ratio, but well water is typically hard and mineral-laden, so it drops scale and depletes the supplemental coolant additives.

Correct answer: The rubber seal is cracked or the relief seat pitted

Replace the cap when the rubber seal is cracked or the relief seat pitted, because it can no longer hold rated pressure and the coolant boils sooner. A vacuum valve that hangs loose when the cap is upturned is normal on many caps and seals once pressure builds. A rubber seal stained with coolant or a discolored spring is cosmetic. A cap that releases at its rated pressure on the tester has passed.

Correct answer: Deep cracks or lost chunks on the glazed ribs

Deep cracks or lost chunks on the glazed ribs mean the belt has lost rib material and grip and must be replaced. Light pilling or rubber crumbs in the grooves are normal on modern EPDM belts and is cleaned off, not a replacement call. A polished sheen on the flat back comes from normal contact with the smooth idler and tensioner pulleys. Fine rubber dust on the ribs is normal while a new belt seats in.

Correct answer: The inner wall is perished and needs a part swap

A hose that squeezes soft and collapses, or has gone hard and brittle, shows the inner wall is perished and needs a part swap before it splits in service. A cap vacuum vent that is stuck can pull a hose flat as the engine cools, but it does not change how the rubber feels in the hand. Slack clamp tension causes seepage at the hose end, not a spongy or brittle body, and a low coolant SCA dose leads to liner pitting rather than hose deterioration.

Correct answer: Black soot or dark tracks at the clamp flange

Black soot or dark tracks at the clamp flange is the clearest evidence of a leak, because escaping gas carries carbon out through the failed joint and paints the path it takes. Dry carbon or ash film inside the stack pipe is normal on a diesel and says nothing about a failed joint. White crust or urea film around the DEF doser is crystallized fluid from a dosing problem, not escaping exhaust. Blue heat tint or straw color at the manifold is normal discoloration on a part that runs very hot.

Correct answer: A leak vents the fumes and harms the cab driver

With the cab over or beside the engine, the safety priority is that a leak vents the fumes and harms the cab driver: exhaust carries carbon monoxide, which is colorless and odorless and seeps into the cab. Lost backpressure for the exhaust brake is a performance concern on any truck, not one the cab position creates. Heat that burns a brake hose under the floor calls for shields and routing, not the gas hazard. A leak that skews exhaust NOx values and derates power is an emissions fault, not a hazard to the person in the cab.

Correct answer: To keep the liners safe from cavitation pits

Nitrite or SCA strips are read to keep the liners safe from cavitation pits: the additive maintains a protective film on the wet liner so the vapor bubbles that collapse against it cannot pit through into the water jacket. Confirming the freeze point of mixed coolant is a refractometer job and is a separate test. Deciding when the next filter renewal falls is driven by hours or mileage, and gauging the pressure lost from the radiator needs a pressure tester, not a chemistry strip.

Correct answer: Low power with black smoke and heavy fuel

A heavily restricted filter starves the engine of air, so the result is low power with black smoke and heavy fuel use: the injected fuel cannot find enough oxygen and leaves as soot. Hard starts with white smoke and misfires point to low compression, cold combustion or fuel problems, not intake restriction. Dusted rings with high blowby and oil use, and worn liners with high blowby, come from unfiltered dirt getting past a torn element or leaking duct; a restricted element is still filtering, it just flows too little air.

Correct answer: It lets grit past the element and scores the bores

A loose clamp on the clean side of the intake must be corrected because it lets grit past the element and scores the bores: dust drawn in downstream of the filter reaches the cylinders and wears rings and liners fast. Keeping the tract sealed from element to turbo to head is a core air-induction check. The defect does not drop the back pressure or lift the fan speed, it cannot heat the coolant or blow off the header hose, and it has no path at all to the batteries or the two cab lamps.

Correct answer: The shaft seal is cracked and the unit is spent

A crusty dried trail below the weep hole means the shaft seal is cracked and the unit is spent, so the pump should be flagged for replacement before the bearing follows it. The weep hole exists to make a failing seal visible early, so a standing trail or stain is a finding rather than the designed behavior, and it is not meant to drip and seep continuously. The residue is a seal problem, so it reports nothing about whether the coolant mix is too rich or the cap is set too high.

Correct answer: Let the engine go cold and crack the cap open slowly

The reliable practice is to let the engine go cold and crack the cap open slowly, because a hot cooling system is pressurized and reading the level cold matches the tank's cold-full mark. Turning the hot cap to the first stop under a rag still vents scalding coolant. Idling the engine and topping the surge tank up with plain water dilutes freeze protection and the additive package, and warming the engine before filling to the brim both opens a pressurized system and overfills it past the cold mark.

Correct answer: Log the oil leak source and grade the repair job

The right action is to log the oil leak source and grade the repair job: oil runs down and back, so the wet pan rail and timing cover only show the path, and the source is the highest wet point found by tracing upward. Logging the pan rail leak and retorquing the pan bolts, or logging a lower pan gasket leak and resealing the pan, both name a downstream point the oil merely runs across. Logging the oil level drop and topping off the crankcase records consumption and leaves the leak unfound.

Correct answer: At the wear index pointer and its travel range

An automatic tensioner is judged at the wear index pointer and its travel range: inside the marked band the arm is still holding the belt correctly, and outside it the belt has stretched or the tensioner spring has weakened, which shows up as slip, noise and undercharging. The coolant surge tank and its static level report cooling, not belt tension. Manifold heat tint is normal discoloration, and the radiator fan pulley bolt torque says nothing about how hard the tensioner arm is pushing.

Correct answer: A hand pumped tester driven to the spec figure

The correct method uses a hand pumped tester driven to the spec figure: the system is brought up to its rated pressure and watched for a drop, then a cap adapter confirms the cap lifts at its stamped value rather than early or late. A glass hydrometer set on the lower drain plug reads coolant concentration and can neither hold nor measure pressure. A test light back probed at the coolant sender checks a circuit, and a vacuum gauge fitted to the intake tract line reads engine breathing, not cooling-system integrity.

Correct answer: A greasy smear of grit at the pressured cooler clamp

The finding that points to a leak is a greasy smear of grit at the pressured cooler clamp. Boost air carries a fine oil mist from the turbocharger, so a split boot, a cracked tube or a slack clamp on the pressure side lets that mist escape and glue road dirt to the joint. A flattened block of fins at the forward cooler face is real impact damage that costs airflow, but bent fins do not vent boost. A moderate warmth of air at the settled cooler tanks is what a charge-air cooler should feel like after a run. A faded bloom of tarnish at the aluminum cooler ends is surface oxidation, not a breach.

Correct answer: The damper rubber is split and its rim has drifted

The clearest reason to replace it is that the damper rubber is split and its ring has drifted, because the elastomer is what bonds the outer inertia ring to the hub; once heat and age break that bond the damper stops absorbing crankshaft torsional vibration, the engine and its accessories take the load, and the timing reference is no longer trustworthy. A shiny track with a slipped belt is a belt or tensioner fault. A faded paint mark with a blurred edge is cosmetic. A tepid shell shortly after shutdown is residual heat, which every damper has.

Correct answer: Sample it hot, from the middle of the stream as the oil drains out

Without a sampling valve, the oil should be at operating temperature so contaminants are suspended, and the sample is caught from the middle of the stream as the oil drains out. Oil pooled in the drain pan picks up residue from the pan and lets heavy debris settle, so it no longer represents the sump. Cold oil from the first or last of the drain carries the water and sludge that settled to the bottom, which skews the report.

Correct answer: Sodium and potassium with glycol on the oil analysis report

Sodium and potassium with glycol on the oil analysis report point to coolant contamination, which also raises the oil level but calls for a cooling-system leak search rather than a fuel-system repair. Low viscosity, a lowered flash point, a diesel odor and thin oil are the classic signs of fuel in the oil. Long idling and frequent active regenerations, which use late fuel injection, are known causes of fuel dilution, so they support it rather than rule it out.

Correct answer: Check this truck's tank cap seal and vent, then drain its tank sumps

Because the other trucks on the same pumps stay dry, the water is entering this tractor's own tanks, so the technician should check this truck's tank cap seal and vent, then drain its tank sumps. A worn cap seal or damaged vent lets rain and condensation in. Sampling the bulk tank would be right if the whole fleet showed water, but the evidence rules out the supply. Shortening the element interval or adding conditioner treats the symptom and leaves the entry point in place.

Correct answer: Technician A is wrong and Technician B is right

Technician A is wrong and Technician B is right. Fuel poured into the secondary filter goes straight to the clean side, so any dirt in it reaches the high-pressure pump and injectors unfiltered; engine makers direct that the final filter be installed dry and primed. Cycling the key lets the electric lift pump push fuel through both filters and purge the air before cranking, which is the approved priming method.

Correct answer: A dust-loaded element with its pleats packed solid by fine dirt

A dust-loaded element with its pleats packed solid raises intake restriction, so it cannot explain a near-zero reading. A split element or a loose clamp downstream of the filter lets unmetered air in, so the vacuum at the tap stays low while dirt reaches the turbo. A failed gauge or a pinched sensing line can also read zero no matter what the filter is doing.

Correct answer: Drain and flush the tank, then refill it with fresh certified DEF

Specification DEF is 32.5 percent urea (about 31.8 to 33.2 percent), so a 19 percent reading from an unknown source means the fluid is contaminated, and the tank should be drained and flushed, then refilled with fresh certified DEF. Topping off only blends the unknown fluid with good DEF and leaves whatever was in the jug in the system. A parked regeneration burns soot in the DPF and does nothing to the DEF in the tank.

Correct answer: Technician A is right and Technician B is wrong

Technician A is right and Technician B is wrong. A leaking EGR cooler lets coolant pass into the exhaust gas that is routed back to the intake, so coolant disappears with no external drip and burns off as sweet-smelling white vapor. A leaking DEF injector loses DEF, not coolant, and leaves white crystal deposits at the injector rather than lowering the coolant level.

Correct answer: Adjusting cab ride height

The cab air springs are fed through their own height-control valve, so the system exists for adjusting cab ride height and isolating the cab from frame motion. Latching cab to the frame is the job of the mechanical cab latches, which hold a tilt cab down and are not air springs. Lowering frame for hookup is done by dumping the chassis air suspension, and leveling frame under load is the chassis leveling valve on the drive-axle air springs, a separate circuit from the cab.

Correct answer: Cab air filter

The cab air filter sits in the fresh-air intake path and traps dust and pollen before the blower pushes outside air into the cab. A cab recirc air filter and a sleeper recirc air filter clean air that is already inside the cab or sleeper and being recirculated, not outside air being drawn in. The engine air filter cleans intake air for combustion and never feeds the cab ventilation system.

Correct answer: Disconnecting battery cables and wearing protective gear

Work in an open engine bay starts by killing the electrical source and putting protection on, so disconnecting battery cables and wearing protective gear is the measure called for. Positioning hydraulic jacks and releasing parking brakes removes the only thing holding the vehicle still; pressurizing coolant hoses and inspecting radiator seams is a leak test rather than a precaution; energizing accessory circuits and logging sensor outputs leaves the system live while hands are inside it.

Correct answer: Opening engine maintenance access

Swinging the cab forward clears the whole power unit, so the system exists for opening engine maintenance access for service and repair work. Isolating sleeper berth vibration is what the cab mounts and cab suspension provide; adjusting steering wheel geometry is a tilt-and-telescope column feature; distributing chassis axle loading depends on suspension and fifth-wheel placement.

Correct answer: Isolating shock and absorbing vibration

Cab mounts sit between the cab and the frame rails, isolating shock and absorbing vibration so road and chassis movement is not passed into the cab. Damping engine torque and gearbox shake is the job of the engine and transmission mounts. Damping hood bounce and supporting tilt is handled by the hood mounts and the tilt-assist springs or struts. Locking the cab down and resisting tilt is the cab latch on a tilt-cab truck, not the mounts.

Correct answer: Unsecured hood and serious safety hazard

A malfunctioning hood latch leaves an unsecured hood and serious safety hazard, because the hood can lift at road speed and block the driver's view. An unpropped tilted hood and a crush hazard comes from a failed hood stop or strut, not the latch that holds the hood closed. An unpropped tilted cab and a crush hazard is a failed cab tilt lock on a cab-over. An unlatched cab and a forward-pitch hazard comes from the cab hold-down latch, a different latch on a different truck design.

Correct answer: Cab tilt cylinder

The cab tilt cylinder is the hydraulic ram that lifts the cab clear of the power unit and lowers it back down under control. A cab hinge bracket is the fixed pivot the cab swings about but supplies no force; a cab latch striker only holds the cab down in the traveling position; a cab heater blower moves air through the climate ducts.

Correct answer: Retaining tilted cab position safely

The tilt lock is a mechanical stay that engages once the cab is raised, retaining tilted cab position safely while a technician works beneath it. Securing the lowered cab to the rear latches, and securing the lowered cab for road travel, are both jobs of the cab hold-down latch, which works only when the cab is down. Holding the cab level on its air springs is done by the cab height control valve, not by any part of the tilt system.

Correct answer: Securing raised cab supports and applying lockout tags

Securing raised cab supports and applying lockout tags is the required precaution, because a raised cab must rest on its mechanical support with the controls locked out. Holding the raised cab on the tilt cylinder lock valve relies on hydraulics that can bleed down. Holding it on floor jacks and tagging keys, or bracing it on floor jacks with pump shut, uses a lifting tool rather than a rated support, which can slip or sink.

Correct answer: Record the webbing as defective, because the damage forces replacement

Cut or frayed load-bearing webbing is a defect, so the technician should record the webbing as defective, because the damage forces replacement of the belt assembly. Recording the latch plate as defective because the cut damage borders it blames hardware that is undamaged; the webbing is what failed. Recording the buckle as defective because cut damage reaches its latch condemns a part the stem says still latches and releases. Recording the webbing as a watch item because the buckle still functions treats a cut belt as tolerable wear, and no inspection standard allows a cut in seat belt webbing.

Correct answer: A power-driven system that holds the specified sweeping speed range

The federal minimum is a power-driven system that holds the specified sweeping speed range. 49 CFR 393.78 requires a wiping system meeting FMVSS No. 104, which mandates power operation at two speeds, the higher at least 45 cycles per minute and the lower at least 20, whatever the engine load. A hand-cranked system that brushes the driver side windshield clear fails whatever the driver manages with it, because the standard forbids hand operation outright. A thermostatic blade system that resists the coldest winter buildup is a cold-climate comfort option, never a federal minimum. A washer fluid system that saturates the windshield before sweeping is a separate requirement and says nothing about whether the wipers themselves operate.

Correct answer: Fail the mirror, since the split glass wrecks vision

The technician should fail the mirror, since the split glass wrecks vision: FMCSA rules call for a rear-vision mirror on each side that gives the driver a clear view to the rear, so the mount must be secured and the glass replaced. Tightening the mount because a crack is a cosmetic fault leaves a defective mirror in service. Tightening the mount and leaving the glass as a driver's job also leaves the defect in place. Declaring the truck out of service confuses PMI repair standards with roadside out-of-service criteria, which do not list a cracked mirror.

Correct answer: A worn gas-charged lift strut

The likely cause is a worn gas-charged hood lift strut, the hood support cylinder, which loses its charge and can no longer hold the weight of the hood; as it weakens the hood drifts closed on its own and becomes a crush hazard, so the strut is replaced and the hood then checked to confirm it stays up. A drained hydraulic tilt pump raises a tilting cab, not a hood. A saturated cabin air filter restricts ventilation air. A misaimed lamp adjuster bolt changes where the light points and carries no weight at all.

Correct answer: Technician A is wrong and Technician B is right

Technician A is wrong and Technician B is right. The correct first step for a lit SRS lamp is to retrieve and record the active and inactive SRS codes with a scan tool. Probing airbag circuits with a test light can send enough current to deploy an airbag or set new faults, so manufacturers prohibit it; any circuit testing is done only after the system is disabled per the service procedure.

Correct answer: Technician A is right and Technician B is right

Technician A is right and Technician B is right. An electronic dash gauge reading must be confirmed with a mechanical master gauge before condemning the engine, and a failing sender or a corroded, high-resistance connection is a common cause of a falsely low reading. Treating the dash reading alone as proof of bearing wear risks tearing down a healthy engine.

Correct answer: Two 4 B:C units, each one bracketed, with gauges in the green

Two 4 B:C units, each one bracketed, with gauges in the green, comply: 49 CFR 393.95 allows a non-hazmat power unit either one 5 B:C extinguisher or two extinguishers rated at least 4 B:C each, charged and securely mounted. A single 4 B:C unit is below the one-unit minimum. A 5 B:C unit lying loose fails the mounting rule even though its rating is enough, and a 10 B:C unit reading in the red is not fully charged.

Correct answer: Defect, because flame-producing devices are barred on this tank, loaded or empty

It is a defect, because flame-producing devices are barred on this tank, loaded or empty: 49 CFR 393.95(g) prohibits fusees on any cargo tank motor vehicle used for Division 2.1 or Class 3 materials whether loaded or empty, so this unit needs three bidirectional reflective triangles. Six fusees are a permitted option only on vehicles the flame ban does not cover, and the ban reaches well beyond explosives loads.

Correct answer: Fail it, since the tether holds the seat and belt down during a crash or a rollover

Fail it, since the tether holds the seat and belt down during a crash or a rollover. On an air-suspension seat the lap belt is mounted to the seat, so the tether is what ties the seat and belt to the floor; without it the suspension can extend and let the occupant rise out of the restraint. A belt that latches properly is not enough, and the tether is a restraint item, not a ride-height or air-spring protector.

Correct answer: Two short cracks that run into each other and form an X shape

Two short cracks that run into each other and form an X shape violate 49 CFR 393.60(c), which allows any crack that is not intersected by another crack. A single long crack, however wide it spans, is an allowed exception, and damage that can be covered by a 3/4-inch disc is allowed when it is at least 3 inches from other damage, so the chips four inches apart and the bullseye five inches from another chip pass.

Correct answer: A camera 10 inches below the top edge of the wiper-swept area

A camera 10 inches below the top edge of the wiper-swept area does not comply: 49 CFR 393.60(e)(1)(ii) allows vehicle safety technology no more than 8.5 inches below the upper edge, or no more than 7 inches above the lower edge, of the area swept by the wipers. The 7-inch position was outside the older 4-inch zone but is permitted under the current 8.5-inch limit, and 3 inches below the top and 6 inches above the bottom are within limits.

Correct answer: A plugged fresh-air inlet filter element

A plugged fresh-air inlet filter element is most likely, because it restricts the air entering the HVAC case, so every outlet, including defrost, is weak at all blower speeds. An open speed resistor would kill one or more blower speeds, which the technician ruled out. A mode door stuck at the floor would leave floor airflow strong while other vents are weak, and a stuck blend door changes air temperature, not volume.

Correct answer: The APU hour meter against the APU maker's own hour-based interval

The APU hour meter against the APU maker's own hour-based interval decides it, because the APU runs while the truck is parked and its wear tracks its own operating hours on the schedule its maker sets. Using the right meter against the main engine's oil drain interval is the most tempting error, but the APU is a separate small diesel with its own oil capacity and service schedule. The main engine's idle hours and the tractor odometer record main-engine use, so neither shows how long the APU has run.

Correct answer: Recharging storage batteries

The alternator's primary purpose is recharging storage batteries: once the engine runs it turns belt drive into current that restores the batteries and carries the electrical load. Storing the cranking current is the battery's job, not the alternator's. Energizing the starter motor is done by the batteries through the starter solenoid. Filtering the current spikes is a side effect of the battery acting as a buffer, not what the alternator is for.

Correct answer: Electronic Control Module

In vehicle electronics ECM stands for Electronic Control Module, the computer that reads sensor inputs and commands actuators such as the fuel injectors. Electronic Chassis Module, Electronic Cluster Module and Electronic Climate Module fit the letters but name separate controllers for chassis functions, the instrument cluster and cab climate; none is what the ECM acronym expands to.

Correct answer: Managing engine and transmission operation

The powertrain control module exists for managing engine and transmission operation, combining fuel, timing and shift control in one processor. Managing antilock brakes and traction aids is the job of the ABS electronic control unit. Managing body lights and door lock control belongs to the body control module. Managing the cab heater and A/C blower control is handled by the HVAC control head, not the powertrain module.

Correct answer: Inaccurate temperature gauge readings

A coolant temperature sensor that drifts or fails sends a false value to the cluster and engine module, so the expected result is inaccurate temperature gauge readings. Erratic intake air temperature values come from the separate intake air temperature sensor. Erratic intake boost pressure values trace to the boost or manifold pressure sensor. Inaccurate oil pressure gauge needles trace to the oil pressure sender, a different circuit with no coolant input.

Correct answer: Body Control Module

BCM stands for Body Control Module, the node that runs lighting, wipers, door locks and other body circuits. A brake control module is real but is abbreviated EBCM and manages antilock functions. A blower control module only sets HVAC fan speed. A battery control module is found on hybrid and electric packs and is not what the BCM abbreviation names in a conventional electrical system.

Correct answer: Twelve point six volts

A rested, fully charged twelve-volt lead-acid battery reads about twelve point six volts. Thirteen point two volts appears only as surface charge right after charging, which the stem rules out because the battery has sat. Thirteen point eight volts is a typical float or charging voltage, and fourteen point two volts is alternator charging output with the engine running, not an open-circuit resting reading.

Correct answer: Remove surface charge and leave the battery resting fully undisturbed

The technician must remove surface charge and leave the battery resting fully undisturbed, because only a rested battery gives a true open-circuit reading. Charging leaves an artificially high surface charge, so the battery has to sit, ideally several hours, before its terminal voltage reflects state of charge. Warming the box to elevate electrolyte temperature distorts the figure instead of correcting it. Applying continuous cranking amperage is a load test, not an open-circuit measurement. Increasing engine rpm to interpret alternator charging voltage reads system output rather than battery state of charge.

Correct answer: Nine point six volts

The battery passes when terminal voltage stays at or above about nine point six volts at the end of the test. The carbon pile draws half the rated cold cranking amps for fifteen seconds at fifty degrees Fahrenheit or warmer, and holding that figure or better means the battery is good. Ten point five volts is the deep-cycle discharge cut-off and is far too generous as a cranking criterion. Eleven point two volts is not a recognized load-test threshold. Twelve point six volts is a rested open-circuit reading, which a battery cannot hold while a heavy load is applied.

Correct answer: Roughly three hundred amps

The carbon pile should draw roughly three hundred amps, half of the battery's six hundred cold cranking amp rating, held for fifteen seconds. Barely one hundred amps is far too light to expose a weak cell, so a failing battery would pass the test. Nearly two hundred amps is still well under half the rating and understates the load the starter really imposes. Drawing virtually six hundred amps applies the whole rated cranking current, which over-stresses the battery and is not the specified test load.

Correct answer: Thirteen point five to fourteen point five volts

With the engine at the specified speed and the battery charged, voltage measured at the battery should sit between thirteen point five and fourteen point five volts, which is the regulated band. Twelve point seven to thirteen point three volts sits under that band and indicates output too weak to recharge the batteries fully. Fourteen point eight to fifteen point four volts is above the band and will gas the electrolyte over a long run. Sixteen point one to seventeen point eight volts is a regulator that has lost control and would cook the batteries within a shift.

Correct answer: An undercharging alternator that keeps the battery poorly charged

A steady 12.4 volts with the engine running is rest voltage, so it means an undercharging alternator that keeps the battery poorly charged. An overnight parasitic draw that drains the batteries when parked explains dead batteries, but running voltage would still read about 14 volts. A sulfated battery string that cannot hold the charge it receives, or a failing battery string that cannot accept the alternator charge, would still show regulated voltage while the engine runs.

Correct answer: Load the alternator at test speed with the steady amperage recorded

Maximum output is found when the technician will load the alternator at test speed with the steady amperage recorded on an ammeter or clamp, then compare it with the rating. Loading the alternator at curb idle with the charging voltage recorded runs too slowly to reach full output and reads voltage, not current. Loading the output cables at test speed with the voltage drop recorded is a circuit-resistance test, not an output test. Loading the batteries at curb idle with the AC ripple voltage recorded checks the diodes, not maximum amperage.

Correct answer: The alternator misses its rated amperage and needs urgent replacement

Loaded output far below the rating means the alternator misses its rated amperage and needs urgent replacement or repair. Acceptable voltage at idle with little load hides a weak unit, which is exactly why a current output test under load is what decides capacity. Saying the alternator delivers its rated amperage contradicts the measurement that was just taken. Excess battery charge with a corrected electrolyte does not follow from a low amperage reading and would raise voltage, not lower current. A starter demanding excess current shows up as slow cranking, not as low charging output at test speed.

Correct answer: Technician A is valid and Technician B is wrong

Technician A is valid and Technician B is wrong. A loose or glazed belt lets the pulley slip, so the alternator is never driven fast enough to make full output, and the result is an undercharged battery with dim lights. Reading Technician A as amiss and Technician B as right inverts the physics. Treating both technicians as correct cannot hold, because a slipping belt does affect charging output. Treating both as mistaken discards a sound statement about the effect of belt condition and tension.

Correct answer: A high cable resistance that starves the charging current

A large voltage drop across the cables and grounds means a high cable resistance that starves the charging current. Corroded, loose or undersized connections consume voltage before it reaches the battery, which slows charging and makes starting hard. A slipping drive belt is a genuine charging fault, but it limits how hard the alternator is driven and shows up as low output, not as voltage lost across a cable. A clean cable junction that conducts the charging current is precisely what a low reading demonstrates, so it cannot explain a high one. A high regulator setting drives output up, and that raises voltage at the battery instead of dropping it across the connection.

Correct answer: Clean the terminals, tighten the connections, and secure the hold-down

The correct action is to clean the terminals, tighten the connections, and secure the hold-down, because corrosion adds resistance and a loose battery vibrates until its plates shed or the case cracks. Replacing all four batteries and the hold-down is unjustified, since white powder at the posts does not prove the cases are leaking. Greasing over the corrosion seals the resistance in and defers the loose clamp. Rinsing with soda water and topping off the batteries cleans the posts but leaves the loose hold-down unfixed.

Correct answer: An inoperable headlamp, brake lamp, or tail light

An inoperable headlamp, brake lamp, or tail light is the finding most likely to place the vehicle out of service, because the CVSA criteria single out headlamp, stop and tail lamp function. A failed high beam leaves the low beams that the criteria look at. Marker, identification, backup, tag and fog lamps and a reflector are violations to repair, not out-of-service conditions.

Correct answer: Five hundred feet

Required red rear stop and tail lamps must be visible from at least five hundred feet. Federal lighting requirements set that distance so a following driver has time to react, and an inspector checks color, operation and visibility distance together. One hundred fifty feet and two hundred fifty feet fall far short and would pass a lamp far too dim to warn anyone. Three hundred feet is closer but still under the standard, so a lamp visible no further than that is a reportable defect rather than a pass.

Correct answer: A chafed conductor or loose joint inside the lamp circuit

Flicker that changes when the harness is wiggled points to a chafed conductor or loose joint inside the lamp circuit, a connection that makes and breaks as the trailer flexes. A cracked lens or worn socket seated in one marker lamp affects that single lamp and does not follow the harness. A loose clamp or corroded terminal at the tractor battery would dim every load on the rig. A worn contact or corroded terminal on the headlight knob reacts when the knob is touched, not when the trailer harness is moved.

Correct answer: Technician A is valid and Technician B is wrong

Technician A is valid and Technician B is wrong. A corroded or loose ground adds resistance to the return path, which lowers the voltage reaching every device that shares it, so lights dim, cranking slows and electrical behavior turns erratic. Reading Technician A as amiss and Technician B as right reverses the physics, because current cannot cross a corroded joint into the frame any more easily than it crosses one in a cable. Treating both technicians as correct accepts a false claim about grounds, and treating both as mistaken throws away an accurate one.

Correct answer: High resistance in the starter cables and grounds

With good, fully charged batteries, slow cranking points to high resistance in the starter cables and grounds. A voltage-drop test across the positive and negative circuits while cranking exposes the corroded or loose joint that is robbing the motor of current. Excess voltage in the alternator field and diodes is a charging fault and would not slow a starter fed by charged batteries. Loose hardware in the battery clamps and cradles is a separate defect that the passing load test has already ruled out as the cause. Poor aiming in the headlamp lenses has nothing to do with cranking speed.

Correct answer: Loose batteries shake badly, crack the plates, and chafe the cables

An unsecured battery is a reportable defect because loose batteries shake badly, crack the plates, and chafe the cables; vibration breaks up the plate structure and rubs cable insulation through until it shorts to the box, a fire risk. Sulfation comes from sitting discharged, not from electrolyte sloshing, and sloshing does not drain cells. Battery movement does not build static that arcs the posts and lights hydrogen. A battery's weight is trivial to a truck frame, and shifting it neither strains the frame nor drains the cells.

Correct answer: An overcharging condition that boils the batteries and shortens their life

A steady 15.8 volts with the engine running is an overcharging condition that boils the batteries and shortens their life; regulated output belongs roughly between 13.5 and 14.5 volts, so a failed regulator is the usual cause. A bulk-charging condition after a hard crank stays within the regulator's limit and would not hold steady at 15.8 volts. A sulfated-battery condition accepts little current but cannot push the regulator setpoint that high. An idle-load condition does not raise the setpoint; the regulator holds the same voltage at any load.

Correct answer: The white ground circuit, whose loss dims the whole harness

The large center pin is the white ground circuit, whose loss dims the whole harness, because it is the common return that every trailer lamp's current flows back through. A corroded, high-resistance ground raises voltage drop and starves several lamps at once, which is why it shows as dim, flickering or dead lights across the trailer rather than as one dead function. The auxiliary feed, the left stop feed and the marker feed are separate smaller pins, and losing any one of them takes out only the lamps it serves.

Correct answer: A fusible link, sized below the harness, that severs the path during overload

The component is a fusible link, sized below the harness, that severs the path during overload. It is a deliberately smaller-gauge, specially insulated wire spliced into a high-current feed, and under a sustained overload or short it melts internally before the protected harness can overheat, so a melted-open one means the circuit saw excessive current and the cause must be found before a new link goes in. A ballast strand, wound below the console, that drops the volts during warmup is a deliberate voltage-dropping wire and is not meant to melt. A loose braid, bolted below the rail, that returns the current during service is a ground strap. A fine coil, wrapped below the socket, that pulls the armature during closure is a relay winding, never spliced into a battery feed.

Correct answer: Undo the cables, scrub the posts with soda, refit the ground, and seal the metal

The correct procedure is to undo the cables, scrub the posts with soda, refit the ground, and seal the metal, removing the ground cable first and refitting it last so a slipped tool cannot short the battery to the frame. Pulling the positive first risks that short, plain water does not neutralize the acid, and dry wire-brushing leaves acid on the joint. Leaving the cables fitted and spraying cleaner never reaches the clamp-to-post contact surfaces.

Correct answer: Only Technician B is right

Only Technician B is right. Rubber insulating gloves are inspected and air-tested for pinholes and leaks before each use, because a hole that formed since the last dielectric test is not covered by the date stamp. Technician A is wrong because Class 00 gloves are rated for only 500 V AC / 750 V DC, below an 800 V DC bus; leather protectors guard the rubber against cuts and abrasion but add no voltage rating, so Class 0 (1,000 V AC / 1,500 V DC) is the minimum here.

Correct answer: Recheck the meter on that same live source to confirm it still reads

Recheck the meter on that same live source to confirm it still reads: this completes the live-dead-live test, proving the 0 V reading came from a dead circuit and not from a meter, lead or fuse that failed during the test. A second discharge wait adds nothing, because the wait has already been met and the zero still comes from an unproven meter. Turning the key on can command the contactors closed and undo the isolation, and the 12 V battery check says nothing about whether the HV bus is dead.

Correct answer: A CAT III 1000 V meter with test leads of the same rating

A CAT III 1000 V meter with test leads of the same rating is required: the meter's voltage rating must exceed the 800 V system, and EV high-voltage procedures call for at least a CAT III instrument. A CAT IV 600 V meter has the higher transient category but its 600 V rating is below the bus voltage, so it is not safe here. A CAT III 600 V meter fails on its own voltage rating, and fitting it with 1000 V leads does not help, because the whole measuring set is only as safe as its lowest-rated part.

Correct answer: A dragging starter armature or a tight engine adding mechanical load

A dragging starter armature or a tight engine adding mechanical load is the cause: high current draw with slow cranking means the starter is working against excess load, and that heavy draw is what pulls good batteries below about 9.6 V. High resistance in the positive or ground cable, or a pitted solenoid contact disc, would restrict current, giving a low draw with slow cranking and a battery voltage that stays relatively high.

Correct answer: Both technicians are wrong

Both technicians are wrong. A dragging armature or tight engine raises current draw; a low draw with slow cranking points to resistance in the cables, connections or solenoid contacts. A voltage-drop test is valid only with current flowing, so the ground side must be measured while the engine is cranking; with the key off no current flows and even a badly corroded ground cable reads 0 V.

Correct answer: Loose starter mounting bolts letting the pinion mesh at an angle

Loose starter mounting bolts letting the pinion mesh at an angle is the first check: a starter that shifts on its mount engages the ring gear off-center and with poor depth, which grinds and mills the teeth while cranking speed and voltage stay normal once it engages. A slipping overrunning clutch makes the starter whine and spin without turning the engine rather than mill the ring gear. A pinion held in after start shows as a starter that keeps running after the engine fires, and an open overcrank thermostat stops cranking after long cranking instead of grinding.

Correct answer: An open in the blue auxiliary circuit that carries constant power

An open in the blue auxiliary circuit that carries constant power is the fault: trailer ABS is fed full time through the blue conductor, with the red stop lamp circuit serving as the backup supply, so a module that wakes only on the brake pedal is running on its backup alone. The red circuit is clearly working, because pressing the pedal powers the module and the stop lamps light. An open white ground would kill the module in both conditions and dim or disable the lamps, and the brown circuit feeds the tail and license lamps, not the ABS.

Correct answer: Both technicians are right

Both technicians are right. Front-end damage or a bumper replacement can shift the radar bracket enough to aim the beam off-axis without setting a fault, so the alignment is verified to the OEM procedure before release. The radar is aligned relative to the vehicle, so a bumper sitting out of position must be repositioned first, or the alignment is done against the wrong reference and the automatic braking may not work properly.

Correct answer: Body paint sprayed over the panel that sits in front of the radar

Body paint sprayed over the panel that sits in front of the radar is a defect, because the radar must see through an undamaged, unpainted OEM cover, and paint, bug screens or plates in front of it can block or distort the signal. A radar mounted off center is normal on many trucks as long as its lateral offset is programmed in the software. A lamp that lights at key-on and then goes out is a normal bulb check, and torque-stripe paint on the bracket bolts is a normal witness mark, not paint over the sensor.

Correct answer: Recalibrating the camera, since its aim shifted with the new windshield

Recalibrating the camera, since its aim shifted with the new windshield, is the needed repair: lane departure warning reads lane markings through the windshield camera, and new glass changes the camera's mounting angle and optics enough to require the OEM calibration even when the bracket is reused. Re-aiming the bracket by hand is tempting, but the camera's aim can only be set correctly through the OEM calibration procedure. The bumper radar was not disturbed, and a shade band on correct-spec replacement glass sits above the camera's view, so neither explains the change.

Correct answer: Recirculating ball steering

Recirculating ball steering runs a ball-filled worm and nut inside a steering box and drives a pitman arm out to the linkage, which is exactly the arrangement described. Hydrostatic column steering passes fluid down hydraulic lines and needs no box or pitman arm; articulated pinion steering drives a toothed rack directly, so no pitman arm exists; telescopic linkage steering describes an adjustable shaft rather than a gear type.

Correct answer: Uneven tire wear or cupping

Uneven tire wear or cupping is the classic sign of a suspension problem, because worn shocks, springs and bushings let the tire bounce and scrub. Center tread wear points to overinflation, and bead chafe to a wrong or damaged rim. Both-shoulder wear or a run-flat comes from underinflation. Flat spots or skid-worn tread come from a wheel locking under braking, which is a brake or ABS problem.

Correct answer: Delivering engine torque to driven wheels

The differential's primary purpose is delivering engine torque to driven wheels, turning drive through the ring and pinion and sharing it between the axle shafts while letting them turn at different speeds in a corner. Locking the rear wheels to the axle speed is what a driver-controlled differential lock does, the opposite of normal operation in a turn. Moving engine torque from gearbox to axle is the driveshaft's job, and interrupting engine torque to the gearbox is the clutch's job.

Correct answer: Main transmission

The main transmission takes crankshaft output and multiplies or reduces it through selectable ratios before passing it down the driveline, which is the conversion described here. A turbo intercooler only cools compressed intake air; a differential case divides torque that has already been delivered to it rather than converting engine output; a coolant reservoir simply stores coolant for the cooling circuit.

Correct answer: Resisting cornering body roll

A stabilizer bar ties the two sides of an axle together in torsion, so as the body leans the bar twists and pushes back, resisting cornering body roll. Absorbing braking axle torque is the work of the torque rods and spring hangers; damping vertical wheel motion is what the shock absorbers do; reducing exhaust stack rattle is a question of mounts and clamps.

Correct answer: Carrying weight and absorbing shock

The primary job of a leaf spring pack is carrying weight and absorbing shock: it supports the load and flexes as the axle meets the road. Damping rebound and limiting bounce is the shock absorber's role, damping body roll and limiting sway belongs to the stabilizer bar, and sensing ride height and venting air describes the height control (leveling) valve on an air suspension.

Correct answer: Supplying hydraulic assist pressure

The belt- or gear-driven pump is the source of the system, supplying hydraulic assist pressure to the steering gear. Metering assist fluid to the piston is the job of the rotary control valve inside the gear. Relieving piston pressure at a stop is done by the poppet or unloading valves in the gear near full lock. Cooling return fluid in the cooler is the work of the steering cooler on the return line, not the pump.

Correct answer: Control arm

A control arm fixes the path the wheel follows relative to the frame through suspension travel, so it holds the alignment angles and keeps tread wear even. A shock mount only anchors the damper and sets no angle. A coil spring carries the weight and sets ride height but does not locate the wheel. A stabilizer bar resists body roll in turns and does not hold camber or toe.

Correct answer: To carry the load and cushion the bump shock

A torsion bar is a spring in bar form: it twists as the wheel rises, so it carries the load and cushions the bump shock. Damping rapid wheel hop and slowing the rebound is the shock absorber's work, since a bar has no valving to dissipate energy. Resisting body roll through a hard corner is the stabilizer bar's role, and locating the control arm while taking up torque is the job of the arm's own pivots and the torque rod.

Correct answer: To couple the stabilizer pivot ends with the control arms

Sway bar links are short rods that couple the stabilizer pivot ends with the control arms, or with the axle, so the bar twists when one wheel rises and body roll is checked. Keeping the rear axle square with the chassis crossmember is done by the radius or torque rods, not by a link. Measuring the unloaded ride height of each steered wheel is an alignment and spring job, and cushioning harsh road shocks at the rubber insulators is the damper and mount function; a link only transmits motion.

Correct answer: Motor mounts

Motor mounts (engine and transmission mounts) carry the weight of the engine and transmission and tie that mass to the frame while isolating vibration. Cab mounts and cab air springs carry and cushion the cab body, not the powertrain beneath it. Radiator mounts support only the cooling module at the front of the frame, so none of the three supports the engine and transmission.

Correct answer: Propeller shaft

The propeller shaft, the component commonly called the driveshaft, carries torque from the transmission output back to the rear axle. Drive couplings only join one rotating member to the next and let the shaft run at an angle; they do not span the distance to the axle. The clutch assembly couples the engine to the transmission input, ahead of the shaft, and the flywheel damper absorbs crankshaft torsional pulses inside the bellhousing.

Correct answer: To bear the truck load and soak up road shocks

Coil springs bear the truck load and soak up road shocks, storing the energy of a bump and releasing it as the wheel returns. Holding the front wheels at a set toe angle is steering geometry, adjusted at the tie rods rather than at a spring. Bracing the axle square and true to the frame is the work of radius rods and track bars, and damping wheel hop while cutting the rebound rate is what the shock absorber does; a spring alone would keep oscillating.

Correct answer: Control arm

A control arm pivots at the frame and at the knuckle, so it holds the wheel in place while letting it travel up and down. A shackle pin is only the hinge that lets a leaf spring change length as it flexes, and it carries no wheel location duty. A shock mount anchors one end of the damper, and a Panhard bar locates an axle side to side; none of the three provide the wheel's pivoting link to the chassis.

Correct answer: To damp and steady suspension motion

A shock absorber forces fluid through valving, turning spring energy into heat, so its purpose is to damp and steady suspension motion after a bump. Carrying and spreading suspension loads is the spring's job; a damper supports no static weight. Limiting and controlling suspension roll is done by the stabilizer bar, and adjusting and holding suspension height is set by spring rate or a ride-height valve, not by the damper.

Correct answer: Reduced axle stability and a vague response

A worn control arm bushing lets the arm shift under load, so wheel position changes as the truck rolls and brakes; the result is reduced axle stability and a vague response at the wheel. Increased steer effort with a delayed return points to a dry king pin or a failing steering pump, not to a rubber bushing. Irregular engine idle with a rougher exhaust is a fuel or air fault, and unequal brake balance with a heavier release comes from the foundation brakes or chamber pressures; neither follows from bushing wear.

Correct answer: To feed steering input out to the road wheels

Tie rod ends are the ball sockets at each end of the cross tube, so their job is to feed steering input out to the road wheels while letting the suspension move. Connecting the pitman arm to the steering arm is the job of the drag link. Swinging the pitman arm off the gear's sector is the steering gear's job. Pivoting the knuckle on the kingpin bushings is the kingpin's role; it carries the knuckle but does not pass steering motion across the axle.

Correct answer: Clearly overshot, because the readjustment maximum sits at 2 inches

The brake has clearly overshot, because the readjustment maximum for a standard clamp-type Type 30 chamber sits at 2 inches and the measured stroke is 2-1/8 inches. Under 49 CFR 393.47 a stroke that reaches or passes the readjustment limit means the brake is out of adjustment. The 2-1/2 inch figure is the long-stroke maximum and belongs to a different chamber, so treating this stroke as safely inside would pass a defective brake. The 1-3/4 inch short-stroke figure belongs to a smaller chamber, and nothing here says this one is wholly spent. And 90 to 100 psi is the correct application pressure for the test, so the stroke is perfectly measurable.

Correct answer: Applied pushrod stroke, the brake adjustment figure

Marking the rod, applying the brakes at the specified reservoir pressure and measuring the travel gives applied pushrod stroke, the brake adjustment figure. Comparing that travel with the readjustment limit for the chamber type is what shows whether the brake is in adjustment. Released brake clearance is a lining-to-drum dimension taken with the brakes off and is not what rod travel reports. Slack adjuster length is a fixed lever dimension read with a rule rather than by applying the brakes. Governor cutout pressure is read on the dash gauge as the compressor unloads and has nothing to do with rod travel.

Correct answer: It rotates the brake camshaft and sets the shoe clearances

The answer is that it rotates the brake camshaft and sets the shoe clearances: it is the lever between the chamber pushrod and the splined S-cam, and its adjusting mechanism holds the lining-to-drum gap. Converting brake air into the pushrod's straight push is the brake chamber's job. Returning the shoes to rest when the chamber exhausts is done by the shoe return springs. Speeding the chamber exhaust and the air release is the work of a quick release valve, not the adjuster.

Correct answer: It rotates the shoe rollers and drives the linings outward

The S-cam sits between the shoe rollers, and when the camshaft turns it rotates the shoe rollers and drives the linings outward against the drum. Converting pushrod travel into torque on the camshaft is the slack adjuster's lever action; taking up lining wear to keep pushrod stroke short is the automatic slack adjuster's job; pulling both shoes back off the drum when air is released is done by the shoe return springs.

Correct answer: Technician A is valid and Technician B is wrong

Technician A is valid and Technician B is wrong. An automatic slack adjuster still has to be stroke-checked at every inspection, because a failed automatic adjuster reveals itself as long stroke and would otherwise go unnoticed until the brake is out of adjustment. Routinely backing off and readjusting an automatic unit by hand is improper, masks internal failure and can accelerate it, so reading Technician B as right or valid is mistaken. Reading Technician A as wrong or amiss discards the one statement that reflects correct shop practice.

Correct answer: Turn the adjuster screw until the brake shoe touches, then reverse

The procedure is to turn the adjuster screw until the brake shoe touches the drum, then reverse it about a quarter to half turn for running clearance. Adjusting with the service brakes or the parking brakes applied gives no true reference to shoe contact and leaves the brake dragging or misadjusted once released. Turning the pushrod clevis changes the factory pushrod length and chamber geometry; it is not a stroke adjustment.

Correct answer: One quarter of an inch

The non-steer air drum brake lining limit is one quarter of an inch, measured at the shoe center on a continuous strip lining, under 49 CFR 393.47(d) and the out-of-service criteria built on it. One eighth of an inch is the figure the same paragraph sets for air disc brakes, so reading a drum shoe against a disc pad limit would leave a worn-out lining in service. One sixteenth of an inch is the hydraulic and electric brake figure, and an air-braked tractor never uses it. Seven eighths of an inch is thicker than any lining limit the rule states, since one quarter of an inch is the largest figure in that paragraph, so condemning a shoe at that reading would scrap friction material that is barely worn.

Correct answer: Sight the open inspection slot and measure the thinnest lining

The best practice is to sight the open inspection slot and measure the thinnest lining, or pull the dust-shield plug, then compare it with the minimum limit, because linings wear unevenly and the thinnest spot governs. Measuring the brake pushrod stroke tells you about adjustment, and an automatic slack hides lining wear by taking up the slack. Measuring the inside drum diameter needs the wheel and drum off, which is the disassembly this check avoids. Checking for S-cam rollover only flags linings already worn far past the limit; it gives no measurement.

Correct answer: No lower than sixty psi

Under FMVSS 121 the low air pressure warning device must operate at a pressure no lower than sixty psi. That leaves the driver a usable reserve to bring the vehicle to a controlled stop well before the spring brakes apply on their own. Twenty psi is roughly where those spring brakes begin to set, which is far too late to be a warning at all. Eighty psi and ninety psi both sit inside the ordinary working range of the system, so a device tripping at either figure would sound during normal driving and train the driver to ignore it.

Correct answer: Never above one hundred thirty-five, never below ninety

The governor unloads the compressor at no more than about one hundred thirty-five psi and lets it resume pumping at no less than roughly eighty to one hundred psi, so never above one hundred thirty-five and never below ninety states the working band correctly. Ceilings of one hundred seventy-five and two hundred fifty psi both exceed the reservoir and system design pressure and would stress the whole air system. A floor of forty or forty-five psi lets reservoir pressure fall well below the low-air warning threshold before the compressor restarts, leaving the driver no usable reserve.

Correct answer: Confirm the dryer purges sharply and check the wet tanks for water

A working dryer is verified when you confirm the dryer purges sharply and check the wet tanks for water: a clean purge at governor cut-out and dry reservoirs show the desiccant is removing moisture. A warm heater only proves the freeze-protection element has power, and gauge build time tests the compressor, not the dryer. A warm outlet is normal compressed-air heat, and leak-down tests the system for leaks. A new cartridge says nothing about function, and tank pressure is set by the governor.

Correct answer: Measure the outside diameter or read the stamped number

Chamber type is established by measuring the outside diameter or reading the stamped number on the chamber, because the type number reports the effective square-inch area of the diaphragm. Getting it right matters because the readjustment limit changes with type. Weigh the empty chamber or contrast the recorded weight against a book figure and you learn nothing, since castings vary between manufacturers. Gauge the retracted pushrod and its length only tells you how the brake is adjusted, and count the mounting studs and you find the same pattern shared across several types. To monitor the release speed or judge the escaping exhaust reports on plumbing and valve condition rather than on chamber size.

Correct answer: Cracked housings, audible leaks, loose bands and torn boots

A PMI chamber inspection looks for cracked housings, audible leaks, loose bands and torn boots, all of which are visible or audible from outside the chamber. Worn diaphragms and weak return springs are internal and cannot be judged without disassembly. Worn cam rollers, glazed linings and cracked drums are foundation brake defects at the wheel end, and oily purge, wet tanks and sticking valves point to the air dryer and supply system, not the chamber.

Correct answer: Perfectly acceptable, since the long chamber stroke reaches 2-1/2 inches

The travel is perfectly acceptable, since the readjustment limit for a long-stroke Type 30 chamber reaches 2-1/2 inches and the measured travel is 2-3/8 inches. The 2 inch figure belongs to a standard clamp-type Type 30, so applying it here would condemn a brake that is in adjustment; identifying the chamber correctly is the whole point of the question. The 1-3/4 inch figure belongs to a smaller clamp housing, and nothing in this reading makes the chamber unserviceable. The 2-1/4 inch figure belongs to another chamber again, so the call is not indeterminate once the type is known.

Correct answer: That the spring brakes hold the loaded vehicle firmly

The test proves that the spring brakes hold the loaded vehicle firmly: with the parking control applied, air is exhausted and the power springs apply the drive-axle brakes mechanically. The service brakes need air pressure delivered by the pedal, so they are not what this test checks. Steer axle brakes have no spring brake chambers. Air tanks holding pressure with the engine off is the separate leak-down test, read on the gauge, not by trying to move the truck.

Correct answer: Two psi per minute

For a single straight truck or bus with the service brakes released, allowable static leakage is about two psi per minute. Three psi per minute is the figure for a combination vehicle, and the stem specifies a single vehicle, so it is too generous here. Forty and fifty psi per minute describe a major leak that would drain the reservoirs and set the spring brakes within a couple of minutes. Charge the system, shut the engine down and watch the gauge to measure the drop.

Correct answer: One eighth of an inch

Steering-axle tires must keep at least one eighth of an inch of tread, the four thirty-seconds written into 49 CFR 393.75(b), read in a major tread groove and never at a tie bar, hump or fillet. The front position carries the stricter limit because tread loss there has the most direct effect on steering response and wet traction. One sixteenth of an inch is the two thirty-seconds that 393.75(c) sets for every other wheel position, so applying it to a steer tire would pass a tire the rule condemns. Three eighths of an inch is twelve thirty-seconds, about the tread a new trailer tire carries, so a steer tire reading that deep is only part worn. Five eighths of an inch is twenty thirty-seconds, inside the eighteen to twenty-three thirty-seconds a steer tire leaves the factory with, so treating it as a minimum would condemn nearly every tire in service.

Correct answer: One sixteenth of an inch

Drive and trailer tires need a minimum of one sixteenth of an inch, the two thirty-seconds written into 49 CFR 393.75(c), read in a major tread groove and never at a tie bar, wear indicator or groove fillet, where the rubber is deliberately shallow. One eighth of an inch is the four thirty-seconds that 393.75(b) demands on the steering axle, so applying the steer figure here would condemn drive and trailer tires the rule still allows. Five sixteenths of an inch is ten thirty-seconds, a part-worn reading that the rule never states. Nine sixteenths of an inch is eighteen thirty-seconds, deeper than the tread a new trailer tire carries, so it is a new-tire figure rather than a wear limit.

Correct answer: Gauge the major grooves, avoid the raised bars, and record the shallowest value

The correct technique is to gauge the major grooves, avoid the raised bars, and record the shallowest value, because the tire fails if any point in a major groove is under the limit. Using the average reading hides a low spot that alone makes the tire out of service. Keeping the center reading ignores the shoulder wear that inflation and alignment faults cause. Probing a single groove and logging the mean depth misses the other grooves and still averages away the lowest reading.

Correct answer: Meet the specified torque, follow the star sequence, and use the calibrated wrench

The correct practice is to meet the specified torque, follow the star sequence, and use the calibrated wrench, so clamp load is even and verified. Oiling the mount faces is wrong because the wheel and hub mating surfaces must stay clean and dry. A clockwise order pulls the wheel on unevenly, and skipping the retorque ignores the recheck fleets make after the first miles. Gunning every nut to stall, even in a star order, over-torques it and stretches the studs, and skipping the torque-wrench recheck leaves the clamp load unverified.

Correct answer: Loose, stretched, or cracked bolts with axle drift and spring movement

When the U-bolts are the subject, the inspector looks for loose, stretched, or cracked bolts with axle drift and spring movement, because the U-bolts alone clamp the axle seat to the spring pack and a slack clamp lets the axle shift and the center bolt shear. Dry, worn or stuck shackle bolts with spring eye wear are found at the spring ends, not at the axle clamp. Worn torque rod bushings with axle windup belong to the torque rod check. Bent, rusted or cracked hanger brackets with spring eye play are a frame-hanger finding, so none of those three is what a U-bolt inspection is looking for.

Correct answer: Cracked spring leaves, shifted plates, or broken center bolts

The reportable defect is cracked spring leaves, shifted plates, or broken center bolts, because each one costs load capacity or lets the leaf pack and axle move out of position. Rusty leaves, unpainted clips and rusty U-bolt nuts are surface corrosion with no loss of section. Open gaps at the leaf tips are normal on a pack whose leaves are not under full load. Polished leaves and rubbed contact pads are the normal wear of leaves sliding on each other. Tapered leaves and stepped lengths are how a multi-leaf pack is built.

Correct answer: Technician A is valid and Technician B is wrong

Technician A is valid and Technician B is wrong. A shock absorber that weeps fluid, has a broken mount, or no longer damps must be noted and evaluated for replacement, which is exactly what Technician A describes. Worn shocks let the suspension keep oscillating after a bump, and that oscillation cups the tires and lengthens stopping distances, so Technician B's claim that shocks affect neither tire wear nor control is untrue. Calling Technician A right and Technician B valid, calling Technician A wrong and Technician B amiss, and calling Technician A amiss and Technician B right all endorse that untrue claim.

Correct answer: By rocking the steering joint, noting the split boot, and checking the castle retainer

Tie rod ends are checked by rocking the steering joint, noting the split boot, and checking the castle retainer, because any play other than rotation, a torn boot and a missing cotter pin are the wear signs. Jacking the axle and rocking the tire top to bottom measures kingpin play instead. Counting steering wheel rim lash measures the whole linkage, not the ends. Measuring toe and tie rod length is an alignment check that does not reveal joint wear.

Correct answer: A worn kingpin and its slack bushings

Vertical and horizontal movement past specification at the tire means a worn kingpin and its slack bushings; vertical play comes from worn thrust shims and horizontal play from bushing clearance. A loose tie-rod end and its ball stud shows up only side to side, never top to bottom. A loose drag link and its worn socket shows when the steering wheel is rocked. A seized kingpin gives hard steering and too little movement, and loose caps only let grease out and water in.

Correct answer: About 0.060 to 0.125 inch, reflecting varied maker service limits

The commonly cited figure is about 0.060 to 0.125 inch, reflecting varied maker service limits, and play past the published limit calls for the pin and bushings to be replaced. A band of about 0.002 to 0.005 inch, echoing listed wheel bearing clearance, belongs to a different measurement taken at the hub. About 0.250 to 0.375 inch, allowing heavy loaded chassis movement, is far past any published steer axle limit and would already be an out-of-service condition. About 1.000 to 1.500 inch, marking total steering linkage failure, is gross wear rather than a service limit.

Correct answer: Wear in the gear box, tie rods, drag links, and kingpins

Excessive lash comes from wear in the gear box, tie rods, drag links, and kingpins, because each joint between the wheel rim and the road wheels adds free play. Worn wheel seals, bearings and hubs cause end play and leaks, not rim lash. A weak steering pump, belt, hoses or filter makes steering heavy or noisy rather than loose. Worn spring shackles, U-bolts, hangers and pins affect axle location and tracking, not wheel lash.

Correct answer: Against the maker mark, with the fluid warm, the engine stopped, and the ground flat

The check is made against the maker mark, with the fluid warm, the engine stopped, and the ground flat, because the reservoir markings only mean what they say at the temperature and attitude the manufacturer assumed. Reading cold fluid against the hot mark puts the level low and invites overfilling, whether the engine is shut down or running with the wheels turned. Reading hot, expanded fluid against the cold mark with the engine idling puts the level high and hides a real loss.

Correct answer: Loose or missing bolts, cracked mounts, or excessive coupler shift

The out-of-service finding is loose or missing bolts, cracked mounts, or excessive coupler shift, because the mounting carries the trailer load and a slack or cracked mount can let the coupling separate. A worn or loose jaw bushing is adjusted, and cracked grease fittings are replaced at the next service. A worn or bent release handle that still works, cracked plate paint and rusted rails are repair items. A dry or scored top plate is cleaned and greased, and a stiff release is lubricated; none parks the truck.

Correct answer: One half inch, measured at the coupler interfaces

The widely used criterion is one half inch, measured at the coupler interfaces. More travel than that between the two halves means worn locking jaws or a worn trailer pin, and the trailer can shift or come free. A one thirty-second gap, tiny at the jaw clearances, is a machining figure rather than an enforcement limit and would condemn almost every coupling in service. Two whole inches, generous at the bracket surface, is grossly loose and long past any inspection limit. Treating the movement as endless lateral slack, free at the trailer joints, ignores a criterion that does exist and is enforced at the roadside.

Correct answer: At each scheduled interval, with the maker mileage table, lock jaws and mounts checked

A fifth wheel is serviced at each scheduled interval, with the maker mileage table, lock jaws and mounts checked, so lock adjustment, mounting bolts and top-plate grease are covered on the maker's mileage or time schedule. The annual DOT inspection is far too infrequent for a plate that needs fresh grease every few weeks. A trailer swap calls for a driver's coupling check, not a lubrication and inspection service. Tire rotation is unrelated to fifth-wheel wear and follows a different schedule.

Correct answer: A leaking inboard bearing seal

Dark streaks on the inboard side of the tire, brake and hub come from a leaking inboard bearing seal, which retains the hub oil; once it fails, oil escapes onto the brake. A leaking hubcap window gasket and a leaking axle flange gasket both leak on the outboard face of the wheel, not the inside. A leaking brake wheel cylinder releases clear or amber brake fluid inside the drum, not dark hub oil, and air-braked trucks have none.

Correct answer: Technician A is right and Technician B is valid

Technician A is right and Technician B is valid. An oil-bath hub cap carries a sight glass and a fill line, so both the oil height and any weeping past the cap have to be read at every PMI, which is what Technician A describes. A wheel seal that leaks onto the linings soaks the friction material, cuts braking effectiveness and is a reportable defect, which is what Technician B describes. Because both statements hold, calling Technician A valid and Technician B wrong, calling Technician A wrong and Technician B amiss, and calling Technician A amiss and Technician B right are all incorrect.

Correct answer: Record the crack, note its spot and length, and flag the repair order

The correct action is to record the crack, note its spot and length, and flag the repair order, because a frame crack grows under load and needs an OEM-approved repair, not a PMI fix. Paint-marking the tips to recheck at the next PMI leaves a growing crack in service. Drilling stop holes and returning the truck to work treats a temporary measure as the repair. Welding a fish plate across it during the PMI is an unapproved frame repair that can embrittle the rail.

Correct answer: Cracked frame rails, missing fasteners, or failing welds

The defect is cracked frame rails, missing fasteners, or failing welds, because the rails carry the whole vehicle and its load and a crack or a broken weld keeps growing under flex. Huck-bolted frame joints are the factory's own fastening method, and surface rust or peeling paint is cosmetic. Bolted frame inserts are an approved reinforcement and factory web holes were drilled by the builder, so neither is a defect. Factory frame splices, Huck bolts and undercoated rails are likewise original construction, not damage.

Correct answer: To check, gauge, lubricate, and service the truck before faults grow

A PMI exists to check, gauge, lubricate, and service the truck before faults grow, catching wear while it is small and cheap. Inspecting, signing, logging and certifying the truck for the DOT annual is a compliance task, only one output of a PMI. Swapping filters, belts, hoses and tires by mileage replaces parts regardless of their measured condition. Road testing, scanning and clearing codes before dispatch is a pre-trip check that hides faults rather than preventing them.

Correct answer: They cover the wear-prone chassis parts likely to fail between service visits

These items are on the list because they cover the wear-prone chassis parts likely to fail between service visits, so brakes, tires, steering, suspension, frame and coupling get looked at before a defect becomes a roadside violation. Most of them are static checks made in the shop, not observations from a driven road check. Calling them a distraction from daily fleet duties misses that a defect here takes the truck out of service. And they apply to every in-service truck of any age, not only to fresh factory units still under warranty.

Correct answer: Excessive clearance between the worn jaws and kingpin

Slap on every change between pulling and braking points to excessive clearance between the worn jaws and kingpin: the slack lets the pin slam from one face of the lock to the other, so the technician checks lock adjustment and kingpin wear against the maker's limits. Dry grease between a scored top plate and the trailer apron causes binding, groaning and hard steering in turns, not a fore-and-aft bang. Leaking glad-hand seals cause an audible air leak and pressure loss. Bent pickup ramps make coupling harder but play no part once the kingpin is locked.

Correct answer: Cage the spring with the release bolt and free the chamber

The correct procedure is to cage the spring with the release bolt and free the chamber, so the power spring is mechanically held before any clamp band is loosened. Pulling the parking valve and removing the clamp before caging leaves the spring free to fire as the housing separates. Draining the air tanks and removing the clamp before caging is the same wrong order, and with no air the spring is fully extended. Clamping the housing in a vise does not restrain the spring inside it.

Correct answer: It stops the air from leaving the downstream reservoirs after a fault

The valve stops the air from leaving the downstream reservoirs after a fault. It passes air forward into the primary and secondary tanks but blocks reverse flow, so a supply-side leak or a failed compressor cannot empty the service tanks and the driver keeps the stored air needed to stop. It neither curbs the air from stroking the chamber reservoirs after a release nor has any metering function at all, since a check valve is open or shut and no reservoir is what strokes a brake chamber. It does not drain the air from wetting the supply reservoirs after a stoppage, because removing water is the work of the air dryer and the drain valve on the wet tank. And it never boosts the air from feeding the governor reservoirs after a demand, because a check valve adds no pressure of its own and the governor only tells the compressor when to load and unload.

Correct answer: A small specified band of loose axial travel

The bearing is finally set to a small specified band of loose axial travel, read with a dial indicator after the nut has been seated and then backed off, so the bearing is neither preloaded nor sloppy. A zero clearance set with no detectable drag leaves nothing for thermal growth and runs the bearing hard. A heavy crushed grip that stops the hub turning by hand is severe preload and will overheat and wreck the bearing. Leaving the nut at maximum torque with the lock tight is that same fault taken to its extreme.

Correct answer: Radial play or roughness when the yokes are rocked by hand

Radial play or roughness when the yokes are rocked by hand means the trunnion bearings are worn and the joint must be replaced. End slide or travel when the shafts are telescoped is the normal movement of the slip joint, not a U-joint defect. Fresh grease out of all four seals when lubed is the desired purge result. Bent tubes or a lost balance weight condemn the driveshaft tube, not the universal joint itself.

Correct answer: A live fault in the antilock brakes needing repair

A lamp that stays lit after the bulb check means a live fault in the antilock brakes needing repair: the ABS controller has found a sensor, modulator or wiring problem and is holding the lamp on. A low air level in the brake tanks triggers the low-air warning lamp and buzzer instead. A wheel spin event lights or flashes the separate traction control lamp. A failed driver in the dash cluster is far less likely, because the ABS controller, not the cluster, commands this lamp after the self-check.

Correct answer: A crack running across the flat face or through a bolt hole

The reject defect is a crack running across the flat face or through a bolt hole, because a cracked disc can let the wheel separate under load. A factory weld seam crossing the rim base and drop well is how a steel rim is made, not damage. Light rust weeping from a hand hole where the paint chipped, and light rust staining the drop well where the paint wore thin, are surface corrosion to clean and repaint; neither is a structural reject.

Correct answer: That the pins are fully seated in their bores

After the slider is moved the technician verifies that the pins are fully seated in their bores, because only those locking plungers hold the fifth wheel or tandem in place, and a partly engaged pin can pop out under load. A lock handle held out in its notch means the pins are still released, which is the condition to correct, not confirm. A lock valve that stays open to the plunger keeps air on the pin cylinder and holds the pins retracted. Greasing the rails is routine lubrication and says nothing about whether the slider is locked.

Correct answer: Worn, stretched, or cracked hanger holes with loose spring travel

The reportable defect is worn, stretched, or cracked hanger holes with loose spring travel, because elongated or cracked holes let the spring and axle shift out of location. Spring ends sliding or rocking in slipper hangers is how a slipper-end spring is designed to work. Rubber bushings twist and flex as the spring travels by design, without rotating on the pin. Shackle pins that are wet or greasy after a lube service simply show fresh grease purging past the seals.

Correct answer: A square angle yields the strongest leverage and truest adjustment

The angle matters because a square angle yields the strongest leverage and truest adjustment: mechanical advantage at the slack adjuster is greatest when the pushrod stands roughly perpendicular to the arm at the applied, full-stroke position, so a sharp angle signals misadjustment or a wrong-length component and throws braking force away. The claim that a steepened angle reshapes only the external outline and surface finish treats a mechanical fault as cosmetic. The claim that a sharpened angle raises the reservoir volume and storage capacity is wrong, since those are fixed by tank size. And the claim that a flattened angle regulates the rubber decay and shoulder abrasion confuses brake geometry with tire wear.

Correct answer: Technician A is right and Technician B is right

Technician A is right and Technician B is right. A low pedal that pumps up with no leak means the pistons must travel too far before the shoes meet the drums, the sign of excess shoe-to-drum clearance. On many duo-servo brakes the star-wheel self-adjuster works during reverse stops, so a seized or corroded adjuster lets lining wear open the clearance a little at a time.

Correct answer: 2.5 and 4.0 degrees; out of spec, since they differ by over 1 degree

Because all three parts slope the same direction, subtract: the front joint runs 5.5 minus 3.0, or 2.5 degrees, and the rear joint runs 5.5 minus 1.5, or 4.0 degrees. The two operating angles should be equal within 1 degree, so 2.5 and 4.0 degrees are out of spec and the pinion angle must be corrected. Adding the slopes gives 8.5 and 7.0 degrees, which applies only when components tilt in opposite directions, and a 2-degree allowance is not the standard.

Correct answer: An oil level sitting a half inch below the fill plug hole

An oil level sitting a half inch below the fill plug hole is low and must be corrected, since the level should be even with the bottom of the hole with the vehicle level, but low oil does not push oil past a seal. A plugged breather lets heat build pressure that forces oil past the seals, a grooved yoke surface leaves a path under the new lip, and worn pinion bearings let the yoke run out and open the seal.

Correct answer: The disc facings have worn; restore free pedal at the inner adjuster

Free pedal shrinks as the disc facings wear, because the pressure plate and release bearing move toward the flywheel and close the 1/8 in. gap between the release yoke and the bearing, so the wear is taken up at the clutch's inner (internal) adjuster. Restoring free pedal at the linkage rod only hides the wear and also upsets the release-bearing-to-clutch-brake gap; the linkage is set once to establish free pedal, not to chase facing wear. A worn clutch brake or release bearing does not steadily reduce free pedal between services.

Correct answer: It is normal gear wear; clean the magnet, refill the axle, and log it

A thin film of fine gray paste is normal wear material from gears and bearings and is exactly what the magnet is there to catch, so the magnet is cleaned, the axle refilled, and the finding recorded. Spalling or pitting sheds visible chips or flakes and is usually heard as noise, neither of which is present. Shortening the drain interval treats a normal finding as a fault.

Correct answer: Draw it warm after the road test, with the tube tip set midway in the oil

A representative sample is drawn warm, right after operation while wear particles are still suspended, with the tube tip about midway in the oil, then sealed in a clean bottle and labeled with the unit, hours or miles, and oil type. A tube resting on the case floor picks up settled sludge, and cold oil has let particles settle. Both the first and the last oil from the drain plug carry a disproportionate share of bottom sediment, so drain-plug samples are a last resort.

Correct answer: The shaft is out of phase; re-index the slip joint so the ears line up

A standard driveshaft is in phase when the yoke ears at both ends line up, so ears 90 degrees apart mean the slip yoke went back on the splines out of phase, which doubles rather than cancels the U-joint speed fluctuation. The fix is to re-index the slip joint to its marked position. A 90-degree offset is the cancelling layout of a CV-style double joint, not of a conventional shaft, and rotating the center bearing does not change the relationship between the yoke ears.

Correct answer: Front 1.5 and rear 3.0 degrees; unequal by more than 1, so it must be fixed

Each working angle is the difference between the driveshaft angle and the component angle: 5.0 minus 3.5 is 1.5 degrees at the transmission and 5.0 minus 2.0 is 3.0 degrees at the axle. The two ends differ by 1.5 degrees, beyond the 1-degree equality the driveline maker calls for, so the speed fluctuations will not cancel and the pinion angle must be corrected. Being under 3 degrees does not make unequal angles acceptable, and adding the angles instead of subtracting them gives the inflated 8.5 and 7.0 figures.

Correct answer: Technician A is right and Technician B is right

Both technicians are right. A master cylinder that leaks past its rear (pushrod) seal sends fluid behind the pedal and under the dash rather than onto the ground, and a slave cylinder that leaks past its piston seal fills its dust boot before any fluid drips. Either leak explains a low reservoir and a soft pedal with a dry floor under the truck, so both places are checked before the reservoir is topped with the fluid type marked on the cap.

Correct answer: Out of limit; the taller tire carries extra load while the shorter one scrubs

A 2 in. circumference gap is about 0.64 in. of diameter (2 divided by pi), far past the commonly cited dual-matching limits of 1/4 in. in diameter or 3/4 in. in circumference. The taller tire carries more than its share of the load and runs hotter, while the shorter tire is dragged along and scrubs irregularly. Treating the 2 in. gap as if it were already under 1/4 in. of diameter is a conversion error, and the same sidewall size does not guarantee matched diameters because wear and brand differences change actual height.

Correct answer: Petroleum oil that got mixed into the glycol brake fluid

Swollen, soft rubber parts throughout the system point to petroleum oil that got mixed into the glycol brake fluid, because brake seal rubber is made to resist glycol fluid and swells when exposed to mineral oil; every rubber part must be replaced and the system flushed. Silicone DOT 5 is the most tempting choice because it must not be mixed with glycol fluid, but silicone does not swell brake rubber. DOT 5.1 is glycol based and compatible with DOT 3, and moisture lowers the boiling point and corrodes bores rather than swelling rubber.

Correct answer: Fluid slipping past worn cups inside the master cylinder bore

A pedal that keeps sinking under steady pressure with no fluid loss points to fluid slipping past worn cups inside the master cylinder bore, an internal bypass that returns fluid to the reservoir. A wheel cylinder leaking into the drum is the most tempting choice because the leak is hidden, but it would still drop the reservoir level. A ballooning hose gives a soft pedal that stops once the hose has swelled, and a failed residual check valve causes a long first stroke or need to pump, not a steady sink under held pressure.

Correct answer: Topping it off with DOT 5 fluid for its higher boiling point

Topping it off with DOT 5 fluid for its higher boiling point is wrong, because DOT 5 is silicone based and must not be mixed with glycol DOT 3 fluid. DOT 5.1 is the most tempting trap in reverse: despite its number, it is glycol based and compatible with DOT 3, as is DOT 4. Discarding an opened can that has sat for a year is correct, because glycol fluid absorbs moisture from the air once the seal is broken.

Correct answer: Corroded slide pins that keep that caliper from sliding freely

Inboard-only wear on one wheel points to corroded slide pins that keep that caliper from sliding freely: the piston pushes the inboard pad, but the caliper body cannot float to pull the outboard pad in, so the inboard pad does all the work. A collapsed hose that traps pressure is the most tempting choice, but with free slides the caliper still floats and both pads on that wheel drag and wear. A seized piston would leave the inboard pad lightly worn, and rotor runout knocks both pads back rather than wearing one side.

Correct answer: The booster is supplying no vacuum assist with the engine running

Pumping the pedal with the engine off deliberately uses up the stored reserve, so when the engine starts a working booster should pull the held pedal down slightly; no movement means the booster is giving no assist, from no vacuum supply, a check valve stuck closed, or a failed diaphragm. A check valve that leaks back only shortens the reserve after shutdown and does not stop assist while the engine runs. An internal master cylinder bypass makes a held pedal sink slowly, not stay put.

Correct answer: Technician A is right and Technician B is wrong

Technician A is right: PTO mounting bolts hold the PTO at the backlash set by its gasket, so loose bolts let the PTO move, change backlash and damage gears or start a leak even before oil appears. Technician B is wrong because equal operating angles cancel the U-joint speed fluctuation only when the yokes on the shaft are also in phase; out of phase, the fluctuations add, hammering the joints, pump shaft and PTO bearings even on a short, slow shaft.

Correct answer: A plugged housing breather, so the seals see pressure hot and vacuum cool

A plugged housing breather explains both findings: the axle builds pressure as it heats, forcing oil past every seal, then draws in moist air and water as it cools, which turns the oil milky. Dry-installed seal lips could explain the seeps but not water in the oil. Mixing compatible gear oil brands does not make lubricant milky; milky oil means water. A worn pinion bearing would account for the pinion seal only, not the wheel-end seals or the water.

Correct answer: Within limit; the lash limit for this 20 in. wheel is 5-1/4 in.

Within limit; the lash limit for this 20 in. wheel is 5-1/4 in. because 49 CFR 393.209 sets separate columns for manual and power steering, and a 20 in. wheel with power steering is allowed 5-1/4 in. at the rim. The 2-1/2 in. figure is the manual-steering limit for a 20 in. wheel, so it does not apply here. The 4-1/4 in. figure is the power limit for a 16 in. wheel, and 5-3/4 in. is the power limit for a 22 in. wheel.

Correct answer: Wear in the steering linkage or ball sockets

Excessive free play at the steering wheel on a road test points to wear in the steering linkage or ball sockets, so the drag link, tie-rod ends and gear lash are checked next. Air in the power steering pump and gear line gives foaming, noise and jerky assist, not lost motion at the rim. Torn shock absorber bushings and worn mounts cause clunks and bounce over bumps. Torn spring shackle bushings and worn pins let the axle shift and the truck wander, but they do not add free play at the steering wheel.

Correct answer: Weak inflation in the cold front tires

Weak inflation in the cold front tires changes rolling radius and drag side to side, so the truck drifts toward the softer tire as soon as the wheel is released. Worn brake linings at both rear wheels shorten lining life and lengthen stops but act evenly, so they produce no steady pull. Scored wheel bearings at the road hubs announce themselves as heat and growl rather than as a drift, and loose tension in the coolant pump belt only costs accessory drive, not tracking.

Correct answer: Worn brake pads

Worn brake pads are the usual source of that squeal: the wear indicator or backing plate contacts the rotor once the friction material is low, and it is heard only while the brakes are applied. A bent brake drum or a bent brake rotor gives a pulsation through the pedal rather than a high-pitched squeal. A leaky brake valve on an air system makes a hiss of escaping air at application, not a friction squeal.

Correct answer: A loose alternator drive belt

A loose alternator drive belt slips as engine speed and electrical demand rise, so output falls just when it should climb and the headlights dim when revved. A shorted cell in the battery drops voltage most at idle and cranking, and revving improves it. A rusty headlamp ground strap dims the lamps at every speed. A corroded battery cable end adds resistance that does not change with engine speed.

Correct answer: Clutch master cylinder failure

Clutch master cylinder failure lets fluid bypass the piston, so the clutch never fully releases and the gears grind as the driver tries to select them. Clutch free play set too small keeps the clutch partly released and causes slipping, the opposite fault. Clutch disc facings badly worn also make the clutch slip under load. Oil-soaked clutch disc facings cause slipping or chatter on engagement; none of those three stops the clutch from releasing for a shift.

Correct answer: A fault in the idle speed control circuit

A fault in the idle speed control circuit leaves the engine unable to hold idle as the truck slows, so it dies when coming to a stop. A fault in the fuel shutoff relay circuit cuts the engine at any speed, not specifically at a stop. A fault in the A/C clutch relay circuit adds or drops compressor load, which a working idle control absorbs. A fault in the vehicle speed sensor circuit upsets the speedometer, cruise and shift logic rather than idle fueling.

Correct answer: Tire imbalance or axle misalignment

Tire imbalance or axle misalignment produces a shudder that comes with road speed because the disturbance repeats with each wheel revolution. Bent fan blades or a loose fan clutch shake the truck with engine speed and can be felt parked at idle. An engine misfire or loose motor mount is also tied to engine speed and load, not to vehicle motion. Out-of-round drums or warped rotors are felt only while the brakes are applied.

Correct answer: A clogged air filter element

A clogged air filter element starves the engine of intake air, so when the pedal goes down the fuel cannot be burned efficiently and the truck responds late. A thermostat stuck wide open makes the engine run cold and slow to warm up, not hesitate on demand. A fan clutch stuck locked on wastes some power and adds fan roar, but it does not delay pedal response. A plugged crankcase breather builds blow-by pressure that pushes oil out of seals, but it does not delay throttle response.

Correct answer: Wheel speed sensor fault at the hubs

A wheel speed sensor fault at the hubs is what lights the warning lamp during braking, because the controller compares the four speed signals and shuts the system down when one drops out or reads erratically. A brake switch relay fault at the dash changes stop lamp and cruise behavior without disabling the controller. An air governor cutout fault at the cab moves compressor cut-out pressure, and a stop lamp filament fault at the rear is a lighting defect; both leave wheel speed data intact.

Correct answer: Worn shock absorbers or loose mount bushes

Worn shock absorbers or loose mount bushes let the axle bounce and the shock body knock on its mounts, so the truck rattles over bumps and rough roads. Worn U-joints or a dry driveline slip yoke cause a clunk on take-off or shifting and a vibration with driveshaft speed. Bent wheel rims or out-of-round drive tires cause a shake that rises with road speed on smooth pavement too. Glazed brake linings or out-of-round drums show up as poor stopping and pulsation only when the brakes are applied.

Correct answer: Low or dirty fluid in the main case

Low or dirty fluid in the main case starves the hydraulic and shift circuits, so gear changes come late and erratically. A clogged or iced breather on the box lets the housing pressurize and push oil past the seals, but it does not delay shifts. A worn clutch brake on the input shaft causes gear clash when selecting a starting gear at a stop. Worn yoke splines on the output shaft produce driveline clunk on take-off, not erratic shift timing.

Correct answer: Technician A is right and Technician B is wrong

Technician A is right: the road speed limit is a customer parameter in the engine ECM, so it is read with service software and then confirmed against the fleet specification and true speed on the road test. Technician B is wrong about the direction: a taller tire makes fewer revolutions per mile, so the ECM undercounts road speed and the truck actually travels faster than its programmed limit, and the speedometer reads low as well.

Correct answer: Taller drive tires were fitted, but the ECM still holds the old tire revs per mile

Taller drive tires were fitted, but the ECM still holds the old tire revs per mile: taller tires turn fewer revolutions per mile, so an ECM using the old, higher value calculates a road speed below the true speed, and both the limiter and the speedometer stop at an indicated 65 mph while the truck really runs 69. Shorter tires with the old value do the reverse, making the ECM overestimate speed so the truck is held below 65. A numerically higher axle ratio left unprogrammed also makes the ECM overestimate speed. Gauge scaling only changes what the dash shows; the limiter works from the ECM's own calculated speed, so it cannot explain a true 69 mph.

Correct answer: Technician A is wrong and Technician B is right

Technician A is wrong and Technician B is right. Cruise control must cancel on the clutch pedal as well as the service brake, because a cruise that keeps fueling with the clutch pushed in lets the engine flare toward overspeed during a shift, so a missing clutch cancel is a defect to write up. Technician B is right because cruise control can only add or cut fuel; with no engine brake working in cruise, gravity can push a loaded truck past the set speed on a grade even when the cruise is healthy.

Correct answer: The engine brake stays applied while the clutch pedal is pushed in to shift

The engine brake stays applied while the clutch pedal is pushed in to shift is the defect, because the clutch switch must deactivate the engine brake during shifts so it cannot drag engine speed down or stall the engine. Dropping out near 1,000 rpm is normal, since the engine controls deactivate the brake at low engine speed to prevent stalling. Staying released with a foot on the throttle and giving less retarding on the low setting are both designed behavior.