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

LOCATION

The Automatic Shut Down (ASD) relay is located in the engine compartment.


PURPOSE

The ASD supplies battery voltage to the fuel pump relay. It also supplies voltage to the fuel injectors, ignition coil, and O2 sensor heating element.


OPERATION

The ground circuit for the ASD relay is controlled by the Powertrain Control Module (PCM). The PCM operates the relay by switching the ground circuit on and off.

The PCM monitors distributor signal to determine engine speed and compute injector synchronization. If the PCM does not receive a distributor signal when ignition switch is in RUN position, it will de-energize (remove ground) from ASD relay. Battery voltage will be cut to the fuel pump relay. It will also be cut to the fuel injectors, ignition coil, and O2 sensor heater element.