Engine Control Module: Description and Operation

ECU Location:

PURPOSE
The electronic control unit (ECU) controls the fuel injection, ignition system and the idle speed system.

BASIC OPERATION
The Electronic Control Unit (ECU) controls the fuel injection system, ignition timing, and the idle speed control system. The ECU also interrupts the operation of the air conditioning and EGR systems, and controls power to the fuel pump (through the control relay).

SELF-DIAGNOSIS
The electronic control unit constantly monitors input and output signals for correct operating range. If an irregularity occurs, the ECU stores a trouble code which can be accessed via the self-diagnosis output terminal. Diagnostic results can be read with a Voltmeter or multi-use tester.

ECU trouble code memory is maintained by direct battery Voltage so diagnostic results are held in memory even if the ignition key is turned off (except for the oxygen sensor code). However, trouble codes will be erased if the battery terminal or the engine control unit connector is disconnected.

CONSTRUCTION
The ECU consists of an 8-bit microprocessor, random access memory (RAM), read only memory (ROM) and an Input/Output (I/0) interface. The ECU is also able to perform self-diagnostic procedures and provide back-up functions if certain circuits fail.

LOCATION
The ECU is located under the glove box.

For additional information, refer to COMPUTERIZED ENGINE CONTROLS.