Engine Control Module: Description and Operation

Detailed Component Locations - Electronic Control Unit:

The electronic control unit (ECU) consists of an 8-bit microprocessor, random access memory (RAM). The ECU actively controls the operation of the fuel injection system, the ignition timing, and has full control of the idle speed control system. The ECU also interrupts the operation of the air conditioning and EGR systems under some conditions, and controls the power to the fuel pump (through the power relay). Based on the information from an array of input sensors (eng. coolant, barometric press., air flow etc.), the ECU determines the optimum control and drives the output actuators accordingly. In addition to this the electronic control unit monitors the input/output signals. When it is noticed that an irregularity has occurred, the ECU memorizes the trouble code, and makes it available to the self-diagnosis output terminal. The diagnosis results can be read out with a Voltmeter or multi-use tester. Moreover, since memorization of the trouble codes is backed up directly by the battery, the diagnosis results are held in memory even if the ignition key is turned off (except for the oxygen sensor code). The trouble codes will, however, be erased when the battery terminal or the engine control unit connector is disconnected.

For diagnosis and testing of the control functions of the fuel injection system, or retrieval of fault codes refer to COMPUTERIZED ENGINE CONTROLS.