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

The [1][2]system relay is a combined function relay. It combines the fuel pump and fuel injection relay into one unit. The system relay provides current to the fuel pumps, suppressor relay, idle air valve, air mass meter, oxygen sensor pre-heating resistor and to other ECU controlled functions or components.

The fuel injection ECU controls the relay ground connection. When ground is supplied, the [1][2]system relay is activated and currant can flow to all the related components. If the ground connection is interrupted, no current can reach the components. This enables the fuel injection ECU to control the fuel pump operation. The fuel pumps are activated only when the ECU receives an engine speed signal. Should the engine stop in case of an accident or other reason, the power supply to the fuel pumps will be interrupted by the system relay, reducing the risk of fire in case of a fuel leak.