Engine Control Module

WARNING: This page is about a different car, the 2003 Saturn LW300 and 2003 Saturn L300. However, it is still accessible from the selected car via links, so may be relevant.

The ECM uses one main microprocessor to control the engine. ECM is located on the left rear of the engine, on the rear intake runner. The main function of the ECM is to control fuel and spark to the engine. The ECM also controls the A/C relay, cooling fan relay, cruise control and generator L-terminal voltage. ECM sends messages to the BCM over the CAN bus to control the coolant temperature gauge, fuel gauge, CHANGE OIL SOON light, CHARGE light, coolant temperature light, LOW FUEL light, MIL, oil pressure light, SERVICE light, speedometer, tachometer and upshift light.

The ECM uses inputs from various sensors, processes the information and commands output devices. It performs diagnostics on both input and output circuits that have associated DTCs. If a circuit fault exists when certain DTC parameters have been met, a DTC will be set and ECM will store Freeze Frame/Failure Record information.