Your FREE ASE T8 Flashcards 2026 – 200+ Cards

A scheduled, systematic check of a commercial vehicle's safety and operating systems to find and document defects before failure or violation — inspect and report, not repair on the spot.

On level ground, a few minutes after shutdown so oil drains back to the pan. Reading while idling or right after shutdown reads falsely low.

Coolant or water in the crankcase — usually a head gasket, cracked head, or leaking oil cooler. Flag for diagnosis; do not just change the oil.

Dark = oxidized/over-extended oil. Milky/tan = coolant contamination. Different problems with different actions.

The most accurate tool for coolant freeze protection; reads the bend of light and is largely unaffected by temperature.

Only about ±8°F and temperature-sensitive — less accurate than a refractometer; ASTM moved to the refractometer method.

A 50/50 mix of ethylene-glycol antifreeze and water gives standard freeze and boil-over protection.

Reduces heat transfer and actually raises the freeze point — never run nearly straight concentrate.

Protects wet cylinder liners from cavitation erosion; level is checked with test strips on a diesel PMI.

Pitting of wet liners caused by collapsing vapor bubbles; prevented by maintaining SCA/nitrite level.

Seals the cooling system and holds pressure to raise the boiling point; a vacuum valve returns coolant from the overflow as the engine cools.

Brittle/cracked sealing gasket or a weak/corroded pressure-relief spring — the cap can no longer hold rated pressure.

Pump the system to its rated pressure to confirm it holds, and use a cap adapter to verify the cap releases at its stamped rating.

A serviceable hose feels firm yet pliable. Spongy/collapsing or hard/brittle = deteriorated — replace before it ruptures.

A crusty dried coolant trail at the weep hole means the shaft seal is leaking — a failing pump.

Glazing, multiple cracks across the ribs, or missing chunks of rib material; EPDM belts also wear thin (check with a wear gauge).

Read the built-in wear-indicator marks; the pointer must fall within the acceptable range or the belt/tensioner is worn.

Black soot streaking around a joint, clamp, or manifold flange where pressurized gas escapes a failed seal.

Carbon monoxide (colorless, odorless) can enter the cab and endanger the driver — repair promptly.

Reduced airflow → low power, black smoke, and higher fuel consumption; replace when the restriction indicator reaches its point.

Lets unfiltered, abrasive air bypass the filter (clean side) and reach the engine, causing rapid cylinder and ring wear.

A gauge/manometer showing intake restriction; tells the technician when the element must be replaced.

Preheat the combustion chamber to aid cold starting by ensuring proper ignition.

Compresses intake air to raise power and efficiency; check for shaft play, oil leaks, and boost-leak signs.

Worn piston rings let oil into the chamber, raising oil consumption and emissions (blue/black smoke).

Routes blow-by gases from the crankcase back to the intake to be burned, relieving pressure and cutting emissions.

Recirculates inert exhaust into the intake to lower peak combustion temperature and reduce NOx.

Trace the wet path upstream to its highest point to find the source, then document the gasket/seal leak and its severity for repair.

Check only when the engine is cool and open the pressurized cap cautiously to avoid scalding; top off with the correct premix, not plain water.

A urea solution injected into the SCR system to reduce NOx; check level and for crystallization/contamination.

Use the dipstick/gauge correctly — the dash temperature gauge shows operating temperature, not coolant level.

Check the intercooler and its hoses/clamps for leaks; a CAC leak loses boost and hurts power and economy.

Support the engine/transmission and absorb vibration; worn mounts cause movement and noise.

Check operation and shroud condition; a fan that won't engage causes overheating under load.

Engine-driven pump that builds the air supply for the brake system; governed by the governor.

Verify pressure at idle and at speed against spec; low pressure can be thin oil, worn pump, or worn bearings.

A diesel naturally compression-ignites; abnormal knock can point to injection timing or mechanical wear — diagnose, don't ignore.

Many diesels use a coolant filter that meters SCA; replace per interval and confirm additive chemistry.

Check alternator, A/C, water-pump, and fan pulleys for wobble, bearing noise, and proper belt tracking.

Must stay sealed end-to-end; any leak on the clean side lets dirt into the engine.

A defect requiring replacement, even if the buckle still latches and releases — webbing damage cannot be compensated by a working buckle.

Belt assemblies must comply with the FMVSS referenced by 49 CFR 393.93; CVSA lists cuts/fraying as defect conditions.

A power-driven (automatic) wiping system that meets its required speeds — a single manual blade does not pass.

Highest speed at least 45 cycles/min and the lower at least 20 cycles/min, regardless of engine load.

Cracks or chips in the driver's critical viewing area can fail; check the swept (wiped) area especially.

Adjusts cab ride height for stability and clearance; check air bags for leaks and the leveling linkage.

Provide isolation and absorb vibration; worn mounts cause noise, movement, and uneven door/hood gaps.

Raises and lowers the cab for engine access; inspect for leaks and proper operation.

Secures the cab in the tilted position during service — must be engaged before working underneath.

Ensure the cab is securely supported and follow lockout/tagout before inspecting the tilt system.

A malfunctioning latch leaves the hood unsecured — a safety hazard that can lead to it opening in motion.

Often aluminum or composite for light weight and corrosion resistance; check mounting and hinges.

Filters fresh-air intake into the cab (HVAC); replace when restricted for ventilation and defrost.

Provides sound insulation and temperature control inside the cab.

Verify all required mirrors are present, secure, and adjustable, and provide the required field of view.

Confirm the horn operates — a required warning device.

Verify oil pressure, coolant temp, air pressure, voltmeter, and warning lamps read and function correctly.

Check cab access steps and grab handles for security and that fuel-tank mounting straps are tight and uncracked.

Doors must latch securely and open/close properly; check weatherstripping and glass operation.

Confirm the defroster clears the windshield — required for visibility in cold/wet conditions.

Confirm washer fluid sprays and the reservoir holds fluid; supports the wiper system.

Check the suspension seat for proper adjustment, function, and secure mounting.

Disconnect the battery and wear appropriate PPE when servicing the engine compartment.

Confirm the backup (reverse) alarm sounds when reverse is selected, where equipped/required.

About 12.6–12.7 V at rest after surface charge dissipates; ~12.4 V is only about 75% charged.

About 13.8–14.4 V — this is charging output, not a resting state-of-charge value.

Remove the surface charge and let the battery rest with no charge or load before reading open-circuit voltage.

Apply about one-half the battery's rated cold cranking amps (CCA) for 15 seconds.

Terminal voltage stays at or above about 9.6 V at the end of the 15-second test (at 50°F+).

Apply about 300 amps (half of 600 CCA) for 15 seconds.

White-green powdery buildup; causes dim lights and slow cranking. Clean and tighten; protect the connections.

Cause dim lights, slow cranking, and odd electrical symptoms — a common, easily missed fault.

Suspect high resistance in the cables/grounds or a worn starter, not the battery.

Batteries must be secured against movement; loose batteries are a defect.

Verify charging voltage and that output supports the loads; dimming when revved suggests a loose belt or weak alternator.

Tail, stop (brake), turn signal, and required marker/clearance lamps plus reflectors — all must function.

Points to a loose connection or ground that intermittently opens — find and secure it.

Verify high/low beams operate and are aimed correctly; both required for night operation.

Headlamps, turn signals, brake lamps, marker/clearance lamps, license-plate lamp, reflectors — confirm all required lamps work.

The governor stops the compressor loading at no higher than about 135 psi.

The compressor resumes building air at no lower than about 80–100 psi.

Engine off, brakes released: max ~2 psi/min for a single vehicle, ~3 psi/min for a combination.

With brakes applied: about 3 psi/min single, 4 psi/min combination.

The low-air warning light/buzzer must activate at about 60 psi.

Time how fast pressure builds from a low reservoir; slow build-up suggests a weak compressor or restriction.

Indicates an ABS fault — the system is degraded/disabled; document and diagnose (often a wheel-speed sensor).

A side-of-trailer ABS lamp works like the dash lamp — lit after bulb-check means a trailer ABS fault.

Feeds wheel speed to the ABS ECU; a bad sensor or air gap commonly triggers the ABS lamp.

Removes moisture from the air supply to protect valves and prevent freeze-ups; check the purge and desiccant.

Drain reservoirs to check for oil or excessive water, which signals air-dryer or compressor issues.

A short can blow fuses or kill an accessory circuit; isolate with a test light/meter and repair the fault.

Use a scan tool to read stored codes rather than guessing the cause of an electronic fault.

A voltmeter reads exact voltage/drops; a test light only shows presence of power — use the right tool.

Verify the parking-brake (spring-brake) control applies and releases the spring brakes properly.

Check the electrical trailer cord and air gladhand connections and seals for damage and secure connection.

Check for corrosion, chafing, loose terminals, and proper routing/securement.

Mark the rod at rest, apply the brakes at ~90–100 psi, then measure how far the rod travels out of the chamber.

Stroke at or beyond the chamber's readjustment limit means that brake is out of adjustment.

A vehicle is out of service when 20% or more of its service brakes are defective (e.g. out of adjustment).

2 inches of applied pushrod stroke.

2-1/2 inches — more travel than the 2-inch standard Type 30.

1-3/4 inches.

2 inches.

1-3/4 inches (standard clamp-type).

2-1/4 inches.

2-3/8" passes a long-stroke Type 30 (limit 2-1/2") but fails a standard Type 30 (limit 2") — identify the chamber before judging stroke.

Connects the chamber pushrod to the S-cam, setting braking leverage and taking up lining wear.

Self-adjusts but must still have stroke checked at PMI — a failing one can let stroke drift out of limit.

Turn the adjusting nut to bring applied pushrod stroke back within spec.

Long stroke on an automatic slack adjuster signals a mechanical problem to diagnose, not a manual readjustment.

The S-shaped cam the slack adjuster rotates to spread the brake shoes against the drum.

The mechanical brake at the wheel (drum-and-shoe or disc) that the air system operates.

Inspect through the inspection slot without full disassembly; condemn when below the minimum lining/pad thickness.

Check for cracks, heat checking, scoring, and that diameter is within the maximum; a cracked drum is a defect.

Inspect chambers for cracks, dents, corrosion, and audible air leaks.

4/32 inch, measured in a major tread groove (49 CFR 393.75).

2/32 inch — less strict than steer axles; measured in a major groove.

Memory aid: steer (front) tires need 4/32", all other (rear) positions 2/32".

Flat tire, audible leak, fabric/cords exposed through the tread, or a regrooved tire on a steer axle.

Generally prohibited on the steer axle of a heavy truck.

Use a tread-depth gauge in a major groove — not on a wear bar or the tread edge.

Check with a gauge against spec; both over- and under-inflation cause uneven wear and failure risk.

Look for cracks, especially at the disc/hand-hole area, bent flanges, and elongated bolt holes.

Rust streaks, shiny wear, or dust 'tails' around lug nuts indicate looseness; torque to spec.

Check for mismatched sizes on duals and cuts, bulges, or sidewall damage.

Seat the bearing, back the nut off, then set a slight specified end play (small axial free movement).

Too tight overheats the bearing; too loose lets the wheel wobble and wear.

Grease or oil at the hub/seal is a defect; inspect for leaks and proper lubricant level on oil-bath hubs.

Check the sight glass/level; low oil or contamination signals a seal or bearing problem.

A broken, shifted, or missing leaf — especially a cracked main leaf — is a reportable suspension defect.

Clamps the leaf spring to the axle; a broken or loose U-bolt lets the axle shift.

Inspect for cracks, wear, and looseness that let the axle move out of position.

Locates the spring on the axle; a sheared center bolt lets the spring shift and the axle move.

Check for leaks, chafing, and cracks; a leaking bag drops ride height and load support.

Maintains ride height on air suspension; damaged linkage causes incorrect height and leveling.

Check for leaks, broken mounts, and that they dampen movement; worn shocks let the suspension rattle/bounce.

Locate the axle fore-aft; worn bushings cause axle misalignment and tire wear.

Raise the axle and pry the tire; vertical play commonly ~0.060–0.125" per OEM spec — beyond it, replace pin and bushings.

Transmit steering input to the wheels; check for looseness, which causes wander and toe wear.

Connects the steering arm to the linkage; check for play and secure, cottered fasteners.

Recirculating-ball steering box and pitman arm transmit steering motion; check for free play and leaks.

Check fluid level, hoses, the pump, and for leaks; the pump provides hydraulic steering assist.

Indicates wear in the gearbox, kingpins, tie-rod ends, or linkage — diagnose the source.

Control arms and bushings hold alignment; uneven or cupped tire wear signals an alignment/suspension problem.

Reduces body roll during cornering; check the bar and end links for damage and looseness.

A crack running up a rail web near a stressed area (crossmember gusset) is a reportable defect — document for repair.

Check rails, crossmembers, and gussets for cracks, bends, loose rivets/bolts, and corrosion.

Loose or missing rivets/bolts at crossmembers and brackets are defects to flag.

Movement over 1/2 inch between the upper and lower halves is out of service — worn jaws or kingpin.

Must fully engage and lock around the trailer kingpin; worn jaws let the trailer separate.

Check mounting bolts/brackets, the pivot, and proper lubrication of the plate.

After repositioning, verify the locking plungers are fully engaged before service/operation.

The pin that locks into the fifth wheel; check for wear, cracks, and proper diameter.

On combination units, check the pintle, lunette eye, and safety chains for wear and security.

Check U-joints for play and the slip yoke for wear; a banging 'slap' on accel/decel signals worn joints.

Check the center support (carrier) bearing and any driveshaft guard for wear and security.

Check axle housings for leaks, the breather, and lubricant level.

Mounted to control the compressor; verify cut-out/cut-in during the brake portion of the inspection.

All brakes should apply together; uneven application or timing causes pull and uneven wear.

Cage the spring brake (or follow the safe procedure) before servicing a chamber so the powerful spring can't release.

Service brakes are air-applied; parking/emergency spring brakes are spring-applied and air-released.

Cycles air pressure to a wheel during ABS events; part of the chassis air-brake electronics.

Check air hoses and tubing for chafing, cracks, kinks, and leaks; secure and away from heat.

Check pad thickness, rotor condition, and caliper/guide-pin operation on air-disc-braked axles.

The readjustment limit depends on chamber type AND size — always match the limit to the chamber.

Excessive lash beyond spec is a defect; measure at the rim with the wheels straight.

Misaligned axles cause dog-tracking and rapid tire wear; check for bent or shifted axles.

Check tank straps, brackets, and for fuel leaks; a fuel leak is a serious defect.

Check that the exhaust is secure, leak-free, and routed away from fuel lines and the cab.

Required where applicable; check for presence and security.

Check the trailer landing gear/dollies for damage, crank operation, and security.

A pushrod operating at a sharp angle to the slack adjuster reduces effective stroke/leverage — inspect geometry.

Look for heat checking and blued drums indicating overheating; investigate dragging brakes.

Oil-bath hubs use a sight glass; grease-packed hubs are inspected for leaks and proper repack.

Worn S-cam bushings cause excessive play and uneven braking — check for radial movement.

Confirm correct ride height; wrong height alters geometry, braking, and driveline angles.

Protects tractor air if a trailer breaks away; verify proper operation during the air check.

Ensures parking brakes apply on air loss; part of the safe-failure design — verify function.

Mismatched dual diameters overload the larger tire and cause scuffing — check and match.

A cracked rim or elongated stud holes is a defect requiring replacement.

Check that the steering gearbox is securely mounted and not leaking.

Check slipper/wear pads at the rear hangers and that leaves aren't excessively rusted or fretted.

Always make the full brake application at about 90-100 psi reservoir pressure before measuring applied pushrod stroke.

On tandem suspensions, the equalizer balances load between axles; check its bushings and pivots for wear.

Confirms braking, steering, shifting, instrumentation, and ride under load, turning symptoms into a component diagnosis.

Low front-tire pressure, brake drag, or an alignment problem causing unequal traction.

Usually worn brake linings/pads — replace.

A loose alternator belt or weak charging system.

Clutch master-cylinder/hydraulic fault or clutch adjustment affecting engagement.

An idle-control problem affecting idle speed/stability.

Tire imbalance/misalignment or driveline (U-joint) wear.

A clogged air filter or fuel-delivery restriction limiting airflow/fuel.

An ABS wheel-speed-sensor or system fault — diagnose with codes.

Worn shock absorbers or loose suspension components.

Transmission fluid level or quality issues affecting performance.

A loose feeling/excess play points to worn steering linkage or components.

Record each defect's location and severity, then a return-to-service, repair, or out-of-service determination.

Check open driver vehicle inspection reports before starting so known defects are verified.

Confirm the truck stops straight and within distance, with no pull, grab, or excessive pedal travel.

If a defect meets FMCSA/CVSA out-of-service criteria, the truck is removed from service until repaired.