Engine Control Module: Description and Operation

PURPOSE/OPERATION
The engine control module controls the fuel injection system, ignition timing, and the idle speed control system. The engine control module also interrupts the operation of the air conditioning and exhaust gas recirculation systems, and controls power to the fuel pump (through the control relay). The engine control module consists of an 8-bit microprocessor, random access memory, read only memory, and an input/output interface.

Based on information from the input sensors (engine coolant temperature, barometric pressure, air flow, etc.), the engine control module determines optimum settings for the output actuators (injection, idle speed, ignition timing, etc.).

The engine 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 self-diagnosis output terminal. diagnostic trouble code results can be read with a voltmeter or multi-use tester.

Engine control module diagnostic trouble code memory is maintained by ignition-off battery voltage so diagnostic results are held in memory even if the ignition key is turned off (except for the oxygen sensor code). However, trouble codes will be erased if the battery terminal or the engine control module connector is disconnected.