General System Description

PURPOSE
The Programed Fuel Injection (PGM-FI) Engine Control Module (ECM) is the primary emission control device. Fuel injection offers precise fuel control over a wide range of conditions. Feedback supplied by the Heated Oxygen Sensor engine sensors allows the injection system to compensate for changes in atmospheric conditions (temperature, altitude, etc.) as well as mechanical conditions (such as state of tune, etc.).

FAIL-SAFE FUNCTION
An array of underhood sensors continually report all aspects of engine operation to the ECM.
If a sensor is perceived by the ECM to be providing inaccurate data, it reverts operation to a pre-programmed value, to allow the vehicle to operate until repairs can be made.
When such a problem occurs, the ECM illuminates the Malfunction Indicator Light (MIL) on the instrument cluster to alert the driver that a fault has occurred and that the vehicle requires service.

BACK-UP FUNCTION
When the ECM is the problem, the fuel injectors are controlled by a back-up circuit independent of the system in order to permit minimal driving.