Computers and Control Systems: Description and Operation

ECM Inputs & Outputs Metro:

The computer command control system, which is controlled by the Electronic Control Module (ECM), is designed to maintain exhaust emission levels at federal standards while providing good driveability and fuel efficiency. The functions of the system are based on data gathered by sensors and switches located throughout the vehicle. The ECM maintains control over fuel delivery, ignition, idle air flow, the fuel pump and other system components, while monitoring the system for faulty operation with its diagnostic capabilities.

The ECM has the ability to do some diagnosis of itself, and of other parts of the system. When it finds a problem, it lights the Malfunction Indicator Lamp on the instrument panel and a trouble code will be stored in the ECM memory. This does not mean that the engine should be stopped right away, but that the cause of the lamp coming "ON" should be checked as soon as reasonably possible.