Craftsman Motor Vehicles Maintenance flashcards

33 cards. Read the term and the definition here. The deck at the top of this page is optional.

Torque wrench usable range

A torque wrench is accurate between roughly 20% and 100% of its rated capacity. Below that range the spring is not loaded enough for reliable readings, so choose a smaller wrench for low-torque fasteners.

Torque-to-yield bolt

A bolt tightened past its elastic limit into plastic deformation, usually to a torque plus a specified angle. It must be replaced each time because reuse leaves it stretched and unable to hold clamp load.

Axle stand placement rule

A hydraulic jack lifts but does not support. Once the vehicle is raised, place axle stands under manufacturer-designated structural points and lower the vehicle onto them before any work beneath it.

Micrometer zero check

Close the micrometer on its anvil with the ratchet stop until it clicks three times, then confirm the reading is zero. Any offset must be recorded and applied to all measurements taken.

Coolant pressure cap function

The cap holds system pressure, raising the boiling point of the coolant by roughly 25 degrees Celsius at 1 bar. A weak cap lets the system boil early, causing overheating under load.

Long-term fuel trim interpretation

Long-term fuel trim above about plus 10 percent indicates a lean condition such as a vacuum leak or weak pump. Below about minus 10 percent indicates a rich condition such as a leaking injector.

Thermostat stuck open symptom

The engine warms slowly, never reaches normal operating temperature, and cools further at highway speed. Fuel consumption rises and heater output falls because coolant circulates constantly.

Diesel high-pressure injection hazard

Common-rail pressure can exceed 1,800 bar. A pinhole leak produces a jet that penetrates skin without pain; this is a surgical emergency, so never crack high-pressure lines to bleed them.

Cylinder leakage test result

With each cylinder pressurised at top dead centre, escaping air locates the fault: intake port means intake valve, exhaust port means exhaust valve, crankcase means rings, radiator means head gasket.

Wet versus dry compression test

A dry test measures compression as assembled. Adding oil to the cylinder seals worn rings, so a large rise on the wet test confirms ring or bore wear rather than valve leakage.

Head gasket failure indicators

Coolant loss with no external leak, white exhaust smoke, bubbles in the expansion tank, emulsion in the oil, and hydrocarbons detected in the coolant all point to a failed head gasket.

Engine bearing knock pattern

A deep knock at half engine speed suggests a main or big-end bearing. A lighter double knock at half speed suggests piston slap, which usually fades as the engine warms.

Clutch slip confirmation

Select a high gear at low road speed and apply full throttle. If engine speed rises without a matching increase in road speed, the clutch is slipping; check free play before removal.

CV joint clicking diagnosis

Rhythmic clicking from a front wheel on full lock under power indicates a worn outer constant-velocity joint. A split boot with grease loss requires replacement regardless of noise.

Automatic fluid level conditions

Check level with the engine running, the selector cycled through all positions, the vehicle level, and fluid at the manufacturer-specified temperature, often between 35 and 45 degrees Celsius.

AWD tyre circumference rule

On permanent all-wheel drive, all four tyres must have closely matched rolling circumference. A significant difference makes the centre differential work continuously, causing overheating and eventual failure.

Spongy brake pedal cause

A pedal that feels soft and compresses further under steady pressure indicates air in the hydraulic system. Bleed in the longest-path-first sequence and check for a fluid leak.

DOT 5 silicone incompatibility

DOT 5 silicone fluid must never be mixed with DOT 3, DOT 4, or DOT 5.1 glycol fluids. They are not miscible, and the mixture causes seal swelling and loss of braking performance.

Brake disc minimum thickness

Each disc carries a minimum thickness marking on the hub. Once measured thickness falls to that value the disc must be replaced, because further machining or wear leaves too little material for heat capacity.

Brake bleed sequence

Bleed the calliper farthest from the master cylinder first, typically right rear, left rear, right front, left front. Vehicles with ABS may need a scan tool to cycle the pump during bleeding.

Caster angle effect

Caster is the rearward or forward tilt of the steering axis. Positive caster improves straight-line stability and self-centring, but excessive positive caster raises steering effort.

Thrust angle misalignment symptom

When the rear axle centreline differs from the vehicle centreline, the steering wheel sits off-centre and the vehicle dog-tracks. Correct rear toe before setting front alignment angles.

Tyre wear pattern meanings

Wear on both shoulders indicates under-inflation; centre wear indicates over-inflation; one-sided wear indicates camber error; feathered tread edges indicate excessive toe on that axle.

Wheel bearing growl test

A hum or growl that changes when the vehicle is swerved left or right indicates a worn wheel bearing, because loading and unloading the bearing alters the noise. Confirm with hub run-out measurement.

Voltage drop test principle

Measure voltage across a cable or connection while current flows. More than about 0.5 volts on a main power or ground path indicates excessive resistance that a resistance measurement alone would miss.

Battery state of charge voltages

At rest, about 12.6 volts is fully charged, 12.4 volts is roughly 75 percent, 12.2 volts is 50 percent, and below 12.0 volts is discharged. Surface charge must be removed before testing.

CAN bus resistance check

With the bus powered down, resistance between CAN-High and CAN-Low is nominally 60 ohms from two parallel 120-ohm terminators. About 120 ohms indicates an open terminator; 0 ohms indicates a short.

Four-pin relay terminal numbers

Terminals 85 and 86 are the coil, 30 is the supply, 87 is the normally open output, and 87a is the normally closed contact. A click with no output means burnt contacts, not a failed coil.

Tyre pressure temperature rule

Tyre pressure rises about 0.1 bar for every 10 degrees Celsius of temperature increase. Always set pressures cold and never bleed a hot tyre down to the cold specification.

Legal tread depth minimum

The legal minimum is 1.6 millimetres across the central three-quarters of the tread. Replace at about 3 millimetres for reliable wet grip, and check for uneven wear and sidewall damage.

Severe service interval rule

Short trips, dusty conditions, towing, and extended idling count as severe service. Under these conditions oil and filter intervals are typically halved and brake and air filter checks shortened.

Diagnostic trouble code meaning

A code identifies the circuit or system that failed a rationality or range test, not the failed component. For example, a cylinder 1 misfire code may result from spark, fuel, compression, or wiring.

Freeze-frame data use

Freeze frame records engine speed, load, coolant temperature, and vehicle speed at the moment a code set. Reproducing those conditions is the fastest route to confirming an intermittent fault.