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

Relay Locations:

The ASD relay supplies voltage to the ignition coil, fuel pump, injectors, and oxygen sensor heating element. It is turned OFF and ON by the engine controller (controls the ground). The Distributor (Hall effect) Signal goes directly to the engine controller, and in the event that the engine controller sees no distributor signal, the ground is removed from the ASD circuit. If the ignition switch is ON and the engine is OFF, the engine controller will allow the ground to be applied to the ASD for approximately 2 seconds, then if no distributor signal is sensed the engine controller removes the ground from the circuit. If the ground is removed from the ASD relay circuit, then the ASD relay acts as an OPEN switch in the power circuits to the fuel injectors, fuel pump, ignition coil, and oxygen sensor heating element, causing a no start condition.