Your FREE ASE G1 Flashcards 2026 – 200+ Cards

Oil's resistance to flow. In 5W-30, the W number is the cold-flow rating and the second number is the thickness at operating temperature.

Flows like a 5-weight when cold (the W) for easy starts and protects like a 30-weight at operating temperature.

A system that estimates remaining oil life from engine data and signals when an oil change is due, replacing a fixed-mileage interval.

Follow the owner's manual or oil-life monitor — commonly 5,000–10,000 miles on synthetic oil; oil degrades by both miles and time.

Park on level ground, shut the engine off, wait a few minutes, then wipe, reinsert, and read the dipstick for an accurate level.

Traps contaminants from circulating oil; replaced with every oil change. A clogged filter can open a bypass and pass unfiltered oil.

Synthetic oil resists breakdown better and usually allows longer change intervals; always use the grade and spec the manufacturer requires.

Delivers the spark that ignites the air-fuel mixture. Worn or fouled plugs cause rough idle, hesitation, and poor fuel economy.

A long-life plug commonly replaced near 90,000–100,000 miles; always confirm the exact interval in the maintenance schedule.

A plug coated with oil, fuel, or carbon that misfires; causes rough idle and poor power and should be diagnosed, not just replaced.

One multi-ribbed belt that drives accessories — alternator, A/C compressor, power-steering pump, and often the water pump.

A spring-loaded pulley that keeps the serpentine belt tight. A weak tensioner causes belt squeal and slipping.

Usually a slipping serpentine belt or a weak/worn tensioner — not always a worn belt.

Modern belts wear by losing rib material rather than cracking; check with a belt wear gauge.

A water-and-glycol mix that transfers heat and protects against freezing/corrosion. A 50/50 mix protects to about −34°C (−29°F).

Check cold at the reservoir; never open a hot radiator or pressure cap — escaping steam can cause burns.

A temperature valve that blocks flow to the radiator until the engine warms. Stuck closed = overheating; stuck open = runs too cool.

Seals and pressurizes the cooling system, raising the coolant's boiling point so the engine can run hotter without boiling.

The belt- or chain-driven pump that circulates coolant through the engine and radiator.

Often a leaking head gasket letting oil and coolant passages mix; refer for deeper repair.

Cleans intake air. A clogged air filter restricts airflow, richens the mixture, and can hurt economy and power.

Positive Crankcase Ventilation — routes blow-by gases from the crankcase back to the intake to be burned, cutting pressure and emissions.

Reads oxygen in the exhaust so the computer can keep the air-fuel ratio near the ideal 14.7:1 (stoichiometric).

The ideal air-fuel ratio for gasoline — about 14.7 parts air to 1 part fuel by weight.

An exhaust device that converts CO, hydrocarbons, and NOx into harmless CO₂, water, nitrogen, and oxygen.

An active misfire severe enough to damage the catalytic converter — stop and diagnose the misfire.

A stored emissions-related fault that is not an immediate threat; retrieve the code and diagnose.

Measures cranking pressure per cylinder to judge sealing of rings, valves, and head gasket; readings should be within about 10%.

Uncontrolled combustion after the spark, from low octane, too much advance, lean mixture, carbon, or overheating; the knock sensor retards timing.

Detects detonation so the computer can retard ignition timing and protect the engine.

Pulls air through the radiator at low speed/idle; an inoperative fan causes overheating in traffic but not at highway speed.

Heat the combustion chamber on a diesel engine to aid cold starting; diesels have no spark ignition.

Keeps the camshaft in time with the crankshaft; a failure on an interference engine can bend valves and stop compression.

Measures intake air so the computer can meter the right fuel; a dirty MAF can cause misfires and poor drivability.

Forced induction; less-than-expected boost is often a wastegate or control-system problem, checked first.

A cylinder failing to fire — from ignition, fuel, or compression loss — causing rough idle, poor power, and a check-engine light.

Unmetered air entering the intake; leans the mixture and causes a rough or high idle.

Sprays metered fuel into the intake or cylinder; a clogged or stuck injector causes a misfire or flooding.

A partially obstructed radiator restricts flow and shows up most under high load and speed.

After an oil/maintenance service, reset the oil-life or maintenance reminder so the system tracks the next interval correctly.

The specified fluid an automatic uses for hydraulic control, lubrication, and cooling. Low or burnt ATF causes slipping and harsh shifts.

Check by the manufacturer's method — dipstick or a sealed check plug at a specified temperature; some units have no dipstick.

A burnt smell or very dark fluid signals overheating and the need for transmission service.

Using a fluid that doesn't meet the manufacturer's spec can cause harsh or erratic shifting.

Causes slipping, delayed engagement, and overheating; it is the first thing to check for transmission complaints.

A fluid coupling that transmits engine power to the transmission and multiplies torque; a slipping converter hurts economy and adds heat.

Locks the converter at cruise to eliminate slip and improve fuel economy.

The gear arrangement inside an automatic that provides the different gear ratios and reverse.

An electrically controlled valve that directs fluid to shift gears; a faulty solenoid can cause harsh or missed shifts.

Regulates line pressure; a defective one causes harsh or erratic shifting.

Causes early, soft shifts because clutches and bands cannot engage firmly.

Strains the ATF; a restricted filter causes delayed engagement and a whining pump.

The hydraulic control center of an automatic; sticking valves (often when cold) cause delayed engagement.

The computer that controls shifting; scanning it for codes helps diagnose electronic shift faults.

Often a loose overdrive band or worn clutch pack — the transmission slips momentarily on the OD shift.

Often sticking valves in the valve body that free up as the transmission warms.

Check ATF level first — a low level is the most common and simplest cause.

Engages reverse gear; a failure can leave reverse inoperative while forward gears work.

Engages forward gears; if not seated, the transmission has no forward movement but reverse may work.

Routes ATF through a cooler (often in the radiator) to control fluid temperature.

Drain-and-fill or full exchange with the specified fluid; follow the maintenance schedule's interval.

A protective default to one gear when the TCM detects a serious fault, to let the vehicle reach a shop.

Connects and disconnects engine power to a manual transmission; lets the driver change gears and start from a stop.

The friction plate clamped between the flywheel and pressure plate; wear causes slipping and a high engagement point.

Clamps the clutch disc to the flywheel; releasing it disengages the clutch.

Pushes on the pressure plate fingers to disengage the clutch; a worn one whines when the pedal is pressed.

Supports the transmission input shaft in the crankshaft; a worn pilot bearing whines with the clutch engaged.

Prevents the clutch from fully releasing, making it hard to shift into all gears; bleed the system.

Matches gear speeds so a manual transmission shifts smoothly; worn synchros cause grinding and popping out of gear.

Often a faulty reverse idler gear — reverse usually has no synchronizer.

Worn or damaged synchronizers (or worn detents) let a manual transmission jump out of gear.

A flexible drive-axle joint that transmits power while allowing steering and suspension movement.

Lets grease out and dirt/water in, destroying the CV joint; inspect boots at every service.

A rhythmic click during tight turns is the classic worn outer CV joint symptom.

Transmits power from the transmission to the rear axle on RWD vehicles; a bent shaft causes a speed-related vibration.

A universal joint that lets the driveshaft flex; a worn U-joint causes a clunk on acceleration and a vibration.

A gearset that lets the drive wheels turn at different speeds, needed because the outer wheel travels farther in a turn.

The differential gears that turn drive from the driveshaft 90° to the axles and provide final gear reduction.

Metal flakes usually indicate failing differential bearings.

The lubricant for manual transmissions, transaxles, and differentials; low level causes noise and wear.

Splits drive to front and rear axles on 4WD vehicles; a defective shift motor can fail to engage 4WD.

A constant hum that changes with vehicle speed (not steering angle), unlike a CV joint click.

Engine RPM rises without matching acceleration; a worn clutch disc or oil-contaminated clutch is the cause.

Keeps gear oil in the differential/axle; a leaking seal causes fluid loss and possible contamination of nearby parts.

The inward/outward tilt of a wheel viewed from the front; excessive camber wears one edge of the tire.

The forward/rearward tilt of the steering axis viewed from the side; controls straight-line stability and steering return, not tire wear.

Whether the tires point in or out; incorrect toe is the most common cause of feathered tire wear.

Toe-in: fronts of the tires point toward each other; toe-out: they point away. Wrong toe scrubs and feathers the tread.

The tops of the wheels tilt outward; excessive positive camber wears the outer edges of the tires.

The tops of the wheels tilt inward; excessive negative camber wears the inner edges of the tires.

Setting camber, caster, and toe to spec for even tire wear and stable handling; required after replacing related parts.

Moving tires between positions for even wear and longer life; pattern depends on drive type and tire directionality.

Inflate to the door-jamb placard pressure, NOT the maximum stamped on the sidewall.

Check when tires are cold — driving heats the air and raises the reading.

Wears both edges/shoulders of the tread and runs the tire hot.

Wears the center of the tread.

A saw-tooth edge pattern caused by incorrect toe.

Uneven dips in the tread from worn shocks/struts or other suspension wear.

Tire Pressure Monitoring System — warns of low pressure; many vehicles need a relearn after tire service.

Direct uses a sensor in each wheel; indirect infers pressure from wheel-speed differences.

A solid light means low tire pressure; a flashing light usually means a sensor or system fault.

Damps spring oscillation; worn shocks cause excessive bounce, nose-dive, and tire cupping.

A combined shock and suspension upright that also serves as a steering pivot, common on front suspensions.

Supports vehicle weight and absorbs road shock; a broken/sagging spring lets a corner sit low.

A stacked-blade spring (often rear); worn leaves let the rear sag.

A pivoting connection between control arm and knuckle; a worn one causes a clunk over bumps and uneven tire wear.

Cushions the control arm pivot; worn bushings cause clunks and alignment changes.

Connects the sway bar to the suspension; worn links rattle/clunk over bumps.

Connects the steering linkage to the knuckle; wear causes excessive steering play and a bent tie rod alters toe.

A common steering gear that converts steering-wheel rotation to side-to-side motion; worn mounts cause a clunk.

Steering-linkage parts in a parallelogram system; wear causes play and wander.

Provides hydraulic assist; a weak pump or low fluid causes hard steering, worst at low speed.

Uses an electric motor instead of a hydraulic pump; no power-steering fluid to service.

Usually unbalanced wheels causing vibration felt through the wheel.

A steering wheel not centered when driving straight, often from a bent tie rod or an uncorrected alignment.

Often worn tie-rod ends or a worn steering gear; inspect linkage first.

Lets the strut rotate with steering; a faulty bearing squeaks/binds during turns.

Supports the wheel and lets it spin; a worn bearing growls and changes with vehicle speed.

Often worn ball joints, control-arm bushings, sway-bar links, or strut mounts.

Adding weights so a wheel/tire spins without vibration; imbalance causes shake at speed.

The vehicle's resting height; a low corner indicates a weak or broken spring.

Dampens steering oscillation (common on trucks); not a tire-wear item.

The pedal-operated hydraulic pump that sends pressurized fluid to all four wheels; an internal leak lets the pedal slowly sink.

A hygroscopic hydraulic fluid (DOT 3/4/5.1) that absorbs moisture, lowering its boiling point; keep capped and change on schedule.

Brake fluid absorbs water over time, which lowers the boiling point and can cause a spongy pedal under heavy use.

Removing air from the hydraulic system to cure a soft/spongy pedal.

Usually air in the hydraulic system; bleed the brakes.

A pedal that slowly drops under steady pressure points to a failing master cylinder (internal leak).

Pads clamp a spinning rotor to stop the wheel; common on front axles and many rears.

The friction material that clamps the rotor; replace as a set per axle when worn.

A metal tab that contacts the rotor when pads are thin, making a high-pitched squeal that warns of replacement.

The disc the pads clamp; a warped or thickness-varied rotor causes a pedal pulsation.

The discard spec stamped on the rotor; a rotor below it must be replaced, not machined.

A rhythmic pulse felt during braking from a warped or uneven-thickness rotor.

Houses the pistons that press the pads against the rotor; a sticking caliper drags and can cause a pull.

Causes a brake drag, uneven pad/dust, and a pull — usually the vehicle pulls toward the OPPOSITE side that is sticking.

A pull to one side under braking, usually a sticking caliper on the opposite side or a hydraulic restriction.

A rear-brake design where shoes press outward against a rotating drum.

The friction parts in a drum brake that press against the drum.

The hydraulic actuator in a drum brake that pushes the shoes out; a leak contaminates the linings.

Keeps drum-brake shoe-to-drum clearance correct as the linings wear.

A mechanical brake (cable or electric) that holds the vehicle; it must be adjusted for proper holding.

A vacuum- or hydraulically-assisted unit that multiplies pedal force; a failure makes the pedal very hard.

Excessive pedal effort with adequate stopping usually means a failed booster or lost vacuum.

Holds vacuum in the booster; a leak gives a soft pedal at start-up that firms once the engine runs.

Pulses brake pressure to keep wheels from locking during hard braking, preserving steering control.

Reports each wheel's speed to the ABS module; a faulty sensor can cause improper ABS operation.

Lights for an ABS fault; first scan for ABS trouble codes before replacing parts.

Loss of braking from overheated pads/fluid; boiling fluid (water-laden) makes it worse.

Balances front/rear brake pressure to prevent rear lock-up under hard braking.

A small held pressure that, if excessive, can cause brakes to drag and not fully release.

Pad/rotor wear dust; much less on one wheel can indicate a seized caliper there.

A wear-indicator squeal at light braking that quiets when the pedal is firmly applied.

Checking lateral wobble with a dial indicator; excess runout causes pulsation.

Stores electrical energy to crank the engine and run accessories when the engine is off.

Adds resistance and can cause slow cranking and starting problems; clean and secure terminals as service.

Secures the battery to prevent vibration damage and shorts; tighten as routine service.

Applies a load to check the battery's ability to deliver cranking current; a conductance tester is also used.

The belt-driven generator that charges the battery and powers loads, typically 13.5–14.5 volts running.

Confirms the alternator keeps the battery charged at about 13.5–14.5 V at idle.

On with the engine running, it indicates a charging-system problem (not just a low battery).

Dimming as RPM drops at idle suggests a failing alternator that cannot keep up at low speed.

Adds resistance and can leave the battery undercharged.

The electric motor that cranks the engine; draws high current through the starter circuit and solenoid.

An electromagnetic switch that engages the starter and connects high current to it.

A control relay in the starting circuit; a defective relay can prevent cranking.

Usually high resistance in the starter circuit — corroded/loose cables or grounds.

Measures voltage lost across a connection under load; above about 0.1 V on a ground means unwanted resistance.

The return path of a circuit; a poor ground causes dim lights, slow crank, and odd electrical faults.

A sacrificial link that opens to protect a circuit from overcurrent; check the fuse first for a dead circuit.

An electrically operated switch that lets a small current control a larger one (fans, fuel pump, starter).

The on-board diagnostics connector for scan tools; check its fuse if the scan tool won't communicate.

A test light shows presence of voltage; a digital multimeter measures exact volts, ohms, and amps.

An unintended low-resistance path that blows fuses or drains the battery.

A break in the circuit that stops current flow; the load won't operate.

Current drawn with the key off that drains the battery overnight; measured in milliamps.

Controls the electric cooling fan; a shorted relay can run the fan constantly.

A common light repair; match the correct bulb type and avoid touching the glass on halogen bulbs.

The fluid (R-1234yf or R-134a) an A/C system circulates to move heat from the cabin to outside; it must be recovered, never vented.

R-1234yf is the newer low-GWP refrigerant in late-model vehicles; R-134a is older. They must not be mixed.

Pumps and pressurizes refrigerant; its clutch engages it. A seized pulley bearing causes noise and belt slip.

Sheds heat from high-pressure refrigerant (like a small radiator) at the front of the vehicle.

Absorbs cabin heat as refrigerant boils; condensation on it drains outside and can grow mold.

Meters refrigerant into the evaporator, dropping its pressure so it can absorb heat.

Refrigerant must be captured with a recovery/recycling machine, never released to the atmosphere.

Checked with manifold gauges; abnormal high/low readings point to charge level or component faults.

Causes poor cooling; bubbles in a sight glass at idle can indicate a low charge.

Mold or mildew growth on the evaporator and case; worsened by a clogged cabin filter or blocked drain.

Cleans air entering the cabin; when clogged it reduces airflow on all settings and can cause odors.

A classic clogged cabin air filter symptom; replace the filter.

Carries condensation outside; a blocked drain leaves water in the case and can wet the carpet.

A small radiator that uses hot engine coolant to warm cabin air.

Causes a sweet antifreeze smell, foggy windows, and sometimes wet carpet.

Controls how much hot coolant/air reaches the cabin; a fault causes poor heat or temperature control.

A motor that positions the blend door for temperature/mode; a failure causes wrong temperature or mode.

Moves air through the HVAC system; a clogged cabin filter strains it and weakens airflow.

Directs airflow to panel, floor, or defrost vents; a vacuum leak can default the system to defrost.

Shuts off the compressor on overpressure; a trip often points to poor condenser cooling (check the fans).

The compressor cycling on/off too often, commonly from a low refrigerant charge.

Directs warm, dehumidified air to the windshield; the A/C often runs in defrost to remove moisture.