Engine Controls - Self-Diagnostics - Without Codes: Introduction: Notes

NOTE: For specific DTC testing, see ON-BOARD DIAGNOSTICS - DISCOVERY & RANGE ROVER article.

The Engine Control Module (ECM) controls engine fuelling using sequential injection to all cylinders. Four double-ended ignition coils provide ignition.

The ECM detects and corrects cylinder knock by advancing or retarding the ignition timing. In the event of a knock system failure a safe ignition map is used.

The ECM uses the inputs from sensors to control engine performance and restrict emissions in line with Onboard Diagnostics II (OBDII). These sensors include a Mass Air Flow (MAF) Sensor, Throttle Position (TP) Sensor, Engine Coolant Temperature (ECT) Sensor and Oxygen (O2) Sensors. The ECM also receives vehicle data, such as road speed from other control modules. The Central Processor Unit (CPU) within the ECM processes all of these inputs, applies correction factors, such as short and long term fuel trim, and issues commands to the engine actuators, injectors and coils.

On vehicles equipped with automatic transmissions the ECM is connected to the automatic Transmission Control Module (TCM) via the Controller Area Network (CAN) bus. The CAN bus conveys data, requests and messages between the control modules. Generally the automatic TCM passes OBD data and requests to the ECM, which stores freeze frame data and activates the Malfunction Indicator Lamp (MIL) when a fault occurs.