Car Terms Glossary

An exhaust emission control device that converts toxic gases and pollutants in exhaust gas into less-toxic substances by catalyzing a redox reaction.

Engine Control Module / Engine Control Unit — the computer that manages engine operation including fuel injection, ignition timing, idle speed, and emissions controls.

Mass Air Flow Sensor — measures the volume and density of air entering the engine to calculate the correct fuel-to-air ratio.

Monitors the oxygen content in exhaust gases to help the ECM maintain the optimal 14.7:1 air-fuel ratio (stoichiometric ratio).

A standardized alphanumeric code stored by the OBD-II system when a vehicle malfunction is detected.

The standardized 16-pin OBD-II port used to connect diagnostic scan tools to the vehicle's computer system.

A snapshot of engine sensor data captured at the exact moment a DTC is stored, providing context for diagnosing the fault.

Exhaust Gas Recirculation Valve — recirculates a controlled portion of exhaust gas back into the engine cylinders to reduce combustion temperatures and NOx emissions.

A system that adjusts the timing of intake and/or exhaust valve events to optimize engine performance across different RPM ranges.

Controller Area Network — a robust vehicle bus standard that allows microcontrollers and electronic control units to communicate without a host computer.

The combined engine and transmission control computer. In many vehicles, the PCM integrates both ECM and TCM functions into a single module.

The Check Engine Light or Service Engine Soon light on the dashboard, officially called the Malfunction Indicator Lamp in OBD-II specifications.