General System Description

System Diagram:

ECU Location:

PURPOSE
The Engine Control Module (ECM) control the fuel injection, ignition timing, and idle speed. In addition it interrupts the operation of the air conditioning and EGR systems and controls power to the fuel pump--through the control relay.

OPERATION
The ECM consists of an 8-bit microprocessor, Random Access Memory (RAM), Read Only Memory (ROM), and an input/output interface.

Based on information from the input sensors--engine coolant temperature, barometric pressure, air flow, etc.--the ECM determines optimum control of fuel injection, idle speed, ignition timing, etc..

SELF-DIAGNOSIS
The ECM constantly monitors input and output signals for correct operating range. If an irregularity occurs the ECM 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.

ECM trouble code memory is maintained by direct battery voltage so diagnostic results are held in memory even if the ignition key is turned off. However trouble codes will be erased if the battery terminal or the engine control unit connector is disconnected.