Glossary
Engine Control Unit (ECU)
The onboard computer that manages fuel injection, ignition timing, and dozens of other engine functions using real-time input from the vehicle's sensors.
Also called the PCM (powertrain control module) on many vehicles. It's the ECU that decides a sensor reading is out of range and stores the resulting DTC — the OBD-II port is just the standardized way of reading what it already knows.
See also
- OBD-II: The standardized on-board diagnostics system, mandatory on US-market vehicles since 1996, that reports diagnostic trouble codes and live sensor data through a common 16-pin connector.
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