Engine Control Module: Description and Operation

PURPOSE/OPERATION
The engine control module operates the fuel injection system and monitors and adjusts ignition timing and the idle speed control system. The engine control module also interrupts the operation of the air conditioning and EGR systems, if needed, and controls power to the fuel pump (through the multiport fuel injection relay).
The electronic control module constantly monitors input and output signals for correct operating range. If an irregularity occurs, the engine control module stores a diagnostic trouble code which can be accessed via the data link connector and a scan tool. Diagnostic trouble codes can also be read using an analog voltmeter.
Engine control module trouble code memory is maintained by direct battery voltage so diagnostic trouble codes are held in memory even if the ignition key is turned off (except for the oxygen sensor code). Diagnostic trouble codes will be erased if the battery terminal or the engine control unit connector is disconnected.