ASE A8 key terms

A stored alphanumeric code set by the control module when a monitored circuit or system performs outside its expected range for a defined time.

A snapshot of sensor and operating data saved when a fault sets, helping a technician see conditions present at the moment the problem was detected.

Live sensor, actuator, and calculated values displayed by a scan tool while the engine runs, used to compare actual operation with expected values.

A diagnostic device that communicates with vehicle control modules to read codes, view live data, perform tests, and sometimes program or relearn components.

The computer that manages engine fuel, ignition, emissions, and transmission functions by reading sensors and controlling actuators based on programmed strategies.

A control mode where the computer commands fuel and spark from programmed tables without using oxygen sensor feedback for correction.

A control mode where the computer uses oxygen sensor feedback to adjust fuel delivery and keep exhaust composition near the targeted value.

A temporary fuel correction percentage the computer applies immediately in response to oxygen sensor feedback, showing how far current fueling is from target.

A learned fuel correction percentage stored by the computer over time to compensate for persistent lean or rich conditions during normal operation.

A sensor that measures the mass of air entering the engine, allowing the computer to calculate the correct fuel mass for current operating conditions.

A sensor that measures intake manifold pressure, which the computer uses with other inputs to estimate engine load and air charge.

A sensor that reports throttle plate angle or position to the computer, used for fuel, ignition, transmission, and idle control strategies.

A sensor that measures engine coolant temperature, allowing the computer to adjust fuel enrichment, ignition timing, idle speed, and closed-loop entry.

A sensor in the exhaust stream that produces a voltage or current signal indicating oxygen content, which the computer uses to judge fuel mixture.

A wide-range exhaust gas sensor that reports a broad air-fuel ratio through a current signal, allowing precise mixture measurement for fuel control and diagnosis.

A sensor that detects crankshaft speed and position, giving the computer the timing reference needed for ignition and fuel injection.

A sensor that detects camshaft position, allowing the computer to identify cylinder stroke and synchronize sequential fuel injection and ignition.

A transformer that steps up battery voltage to the high voltage needed to jump the spark plug gap and ignite the compressed air-fuel mixture.

A threaded component that provides a gap for a high-voltage spark to ignite the compressed air-fuel mixture inside the combustion chamber.

The crank angle at which the spark occurs relative to top dead center, controlled by the computer to balance power, efficiency, and emissions.

A sensor that detects abnormal combustion vibration in the engine block, allowing the computer to retard timing and protect the engine from damage.

A failure of a cylinder to burn its air-fuel charge completely or at the proper time, often detected through crankshaft speed fluctuations.

An electrically operated valve that sprays a measured amount of fuel into the intake port or cylinder under pressure from the fuel system.

A device that controls fuel pressure supplied to the injectors, often by returning excess fuel or varying pressure based on intake manifold vacuum.

A computer-controlled valve that opens to allow stored fuel vapor from the charcoal canister to be drawn into the intake for burning.

A sealed fuel vapor storage and recovery system that captures refueling and evaporation vapors in a canister and routes them to the engine for combustion.

An exhaust component coated with precious metals that promotes chemical reactions converting hydrocarbons, carbon monoxide, and nitrogen oxides into less harmful gases.

A valve that meters exhaust gas back into the intake under certain conditions to lower combustion temperature and reduce nitrogen oxide formation.

A system that routes crankcase vapors into the intake for burning, using manifold vacuum and a metering valve to prevent pressure buildup.

A system that pumps air into the exhaust during cold start to help the catalytic converter heat quickly and reduce hydrocarbons and carbon monoxide.

A test that measures pressure developed in each cylinder during cranking, helping identify leaking valves, worn rings, or head gasket faults.

A test that applies compressed air to a cylinder at top dead center and measures leakage to locate valve, ring, or head gasket problems.

A gauge connected to intake manifold vacuum that shows engine pumping efficiency and can reveal leaks, restrictions, or mechanical faults.

A diagnostic tool that introduces visible smoke into a sealed system to reveal leaks in intake, exhaust, EVAP, or vacuum components.

A test instrument that displays electrical signals over time, allowing a technician to inspect sensor, injector, and ignition waveforms for shape and timing.

A test that measures exhaust pressure ahead of a restriction, such as a clogged catalytic converter, to check for excessive flow resistance.

The intake assembly containing the throttle plate that controls airflow into the engine, often housing the throttle position sensor and idle control motor.

A computer-controlled valve that bypasses or meters air around the throttle plate to maintain a stable idle speed under changing loads.

Unmetered air entering the intake after the airflow sensor, causing a lean mixture unless the computer can add enough fuel.