Engine Control Module: Description and Operation

FUEL INJECTOR CONTROL

The electronic control unit is located under the front passenger seat. The ECU contains information to calculate basic injector duration based upon engine speed and manifold pressure. After the basic duration information is read from memory, the signal is modified by the ECU in reference to the information provided from the other engine sensors. Once the signal is processed, it is passed on to the fuel injectors which respond by opening for the appropriate amount of time.

ELECTRONIC IDLE CONTROL

The intake manifold mounted electronic air control valve (EACV) is used by the ECU to modify idle speed to compensate for engine load or idle instability caused from cold operation, transmission in gear (A/T), alternator charging or air conditioning compressor operation.

IGNITION TIMING CONTROL

Timing control is controlled much the same as injector duration. The ECU contains a basic program for calculating engine timing based on engine speed and manifold pressure. The base signal is then modified by the various other sensor information before the signal is passed on to the igniter unit to fire the spark plugs.

ECU FAIL-SAFE FUNCTION

If a signal from a sensor is determined to be inaccurate, the ECU ignores the signal and substitutes a preset value allowing the engine to remain running until repairs can be made. The ECU then illuminates the check engine light to alert the driver that a malfunction exists.

BACK-UP FUNCTION

In the event of an ECU failure the fuel injectors are controlled by a back-up system independent of the ECU to permit minimal driving until the vehicle can be repaired.

SELF-DIAGNOSIS

If a sensor begins producing inaccurate information, the ECU illuminates the "Check Engine" warning lamp on the dashboard. Once a failure is noticed, the ECU also stores a fault code in eraseable memory. The fault code is indicated by a LED on the ECU which flashes in accordance to the code number of the fault recorded whenever the ignition is on.