System Description

PURPOSE
The vehicle ECM and sensor and output systems control virtually all aspects of engine operation. This combined control allows the engine to function at optimum performance while maintaining exceptable emission and fuel economy levels.

OPERATION
During normal vehicle operation, the ECM controls fuel, spark and emission systems. In the event of a sensor failure or inconsistency the unit switches to "Fail-Safe" mode. In this mode, certain sensor and output parameters become "fixed" allowing limited operation of the vehicle. In most cases the "Malfunction Indicator" lamp is illuminated and trouble codes are recorded in the ECM long term memory. These alert the operator that a system requires attention and guides the technician towards the failed system.