ASE G1 key terms

A measure of how thick an oil is and how easily it flows at a given temperature. Multigrade oils such as 5W-30 flow thin when cold and stay thicker when hot.

A replaceable canister containing filter media that traps metal particles, sludge, and dirt from the oil before it is pumped back to the engine bearings and moving parts.

A mixture of water and antifreeze that carries heat away from the engine. It raises the boiling point and lowers the freezing point so the cooling system works in all climates.

A temperature-controlled valve in the cooling system. It stays closed while the engine warms and opens at a set temperature to let coolant flow through the radiator.

One wide, ribbed belt that drives the alternator, power steering pump, water pump, and A/C compressor on most late-model engines. An automatic tensioner keeps it tight.

A hydraulic oil made for automatic transmissions. It transmits pressure to apply clutches and bands, lubricates internal parts, and carries heat to the cooler.

A fluid coupling between the engine and an automatic transmission. It multiplies engine torque at low speed and lets the car stop in gear without stalling.

A computer that reads vehicle speed, throttle position, and temperature, then commands shift solenoids and line pressure inside an automatic transmission.

A transmission that uses a steel belt or chain running between two pulleys whose width changes, giving an infinite number of ratios instead of fixed gear steps.

A friction assembly between the engine flywheel and a manual transmission. It engages and disengages power flow so the driver can start from a stop and shift gears.

A bearing that presses against the pressure plate fingers when the clutch pedal is pushed, releasing the disc so engine power no longer reaches the transmission.

A flexible joint at each end of a front-wheel-drive halfshaft. It carries power through a changing angle at constant speed while the suspension moves and the wheels steer.

A gear set that divides engine torque between the drive wheels and lets them turn at different speeds, which is needed when the vehicle goes around a turn.

A suspension design where the shock absorber is built into a structural strut that also locates the wheel. It is common on the front of unit-body cars.

A socket-and-stud pivot that connects a control arm to the steering knuckle. It lets the suspension move up and down while the wheel still steers.

The outer, adjustable end of the steering linkage. It connects the steering rack or gear to the knuckle and is adjusted to set toe during an alignment.

Adjusting camber, caster, and toe so the wheels point where the manufacturer specifies relative to the vehicle and to each other.

Friction material bonded to a steel backing plate. The caliper squeezes the pad against the rotor to slow the wheel.

The rotating iron disc that the brake pads clamp on. It must stay above a minimum thickness and within runout limits to brake smoothly.

A hydraulic housing that holds the brake pads. Fluid pressure pushes one or more pistons out to clamp the pads on the rotor.

A hydraulic fluid rated by DOT number that carries pedal force to the calipers and wheel cylinders. It absorbs moisture from the air and should be replaced on schedule.

A sensor at each wheel that reports how fast the wheel is turning. The ABS module uses those signals to detect and prevent wheel lockup during hard braking.

A check of how much voltage is lost across a cable, connection, or ground while current is flowing. More than about 0.1 volt per connection points to excess resistance.

A test instrument that measures voltage, resistance, and current. A digital multimeter is the basic tool for checking circuits, sensors, and battery condition.

Current a vehicle keeps drawing from the battery after all accessories are off and the modules have gone to sleep. Too much draw causes a dead battery overnight.

A belt-driven generator that makes alternating current, converts it to direct current, and keeps the battery charged while the engine is running.

An electrically operated switch. A small coil current closes contacts that carry the much larger current needed by items like a fuel pump or cooling fan.

The fluid in an A/C system that absorbs heat when it evaporates in the evaporator and releases heat when it condenses in the condenser.

A belt-driven pump that raises refrigerant pressure and temperature so heat can be released at the condenser. It also circulates refrigerant and lubricating oil through the system.

A two-gauge tool with hoses that connects to the high and low service ports of an A/C system to read pressures and to add or recover refrigerant.

A small radiator inside the dash that uses hot engine coolant to warm air blown through it for cabin heat and defrost.

An alphanumeric code a control module stores when a monitored circuit or system fails its self-test. The code names the circuit, not the part to replace.

The check engine light on the dash. It comes on when the powertrain control module sets an emissions-related fault code.

Short- and long-term corrections the PCM makes to fuel delivery based on oxygen sensor feedback. Positive trim means the engine is running lean and needs more fuel.

A sensor in the exhaust stream that generates a signal based on the oxygen left in the exhaust, letting the PCM judge whether the mixture is rich or lean.

A diagnostic device that plugs into the OBD-II connector to read codes, display live sensor data, and command tests on vehicle modules.