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

PURPOSE/OPERATION

FUEL PUMP CONTROL RELAY
The Engine Control Module (ECM) receives a signal emitted from the Crankshaft Position Sensor and turns the Fuel Pump Relay "ON" or "OFF" to control Fuel Pump operation. To improve safety, the Fuel Pump will stop if the Engine stalls with the Ignition Switch "ON".

POWER SUPPLY CONTROL RELAY
When the Engine Control Module (ECM) receives an "ON" signal emitted from the Ignition Switch, current flows through the Main Relay. This turns the Ignition Relay "ON" so that power is supplied to the Fuel Injectors, Mass Air Flow Sensor, Idle Air Control Valve, etc..