Computers and Control Systems: Description and Operation

PURPOSE
The Programed Fuel Injection (PGM-FI) ECM/PCM [1] is the primary emission control device. Fuel injection offers precise fuel control over a wide range of conditions. Feedback supplied by the exhaust gas oxygen sensor and various 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.).

LOCATION
The Programmed Fuel Injection Systems ECM/PCM, is mounted under the carpet on the passenger footwell floor.

FAIL-SAFE FUNCTION
An array of underhood sensors continually report all aspects of engine operation to the PGM electronic control unit (ECM/PCM).
If a sensor is perceived by the ECM/PCM 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/PCM illuminates the Check Engine light 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/PCM is the problem, the fuel injectors are controlled by a back-up circuit independent of the system in order to permit minimal driving.

REMARKS:

[1] M/T-equipped cars use an Engine Control Module (ECM). A/T-equipped cars use a Powertrain Control Module (PCM).