Main Relay (Computer/Fuel System): Description and Operation

Main Relay

The GEMS Engine Management System uses four relays, all located within the Engine Compartment Fusebox:

- ECM Power Supply Relay (Main Relay)
- Fuel Pump Relay
- Ignition Relay
- Starter Motor Relay

The Main Relay supplies power to the ECM with a tap off to feed the fuel injectors and Mass Air Flow Sensor. This relay is controlled by the ECM itself, so that the ECM remains powered up after the ignition is removed and the ECM can record all temperature readings and motorize the Idle Air Control Valve to the fully open position. This is known as the "ECM power down routine". Failure of this relay will cause the ECM to not be switched on, resulting in absence of fuel and spark and therefore a failed start.