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

Fig 5 Power Distribution Center:

PURPOSE
The ASD relay supplies battery voltage to the fuel injectors, electronic ignition coil and the heating elements in the oxygen sensors.


OPERATION
The Powertrain Control Module (PCM) operates the Auto Shutdown (ASD) relay by switching the ground path on and off.

The PCM controls the relay by switching the ground path for the solenoid side of the relay ON and OFF.
- The PCM turns the ground path off when the ignition switch is in the OFF position unless the 02 Heater Monitor test is being run.
- When the ignition switch is in the ON or Crank position, the PCM monitors the crankshaft position sensor and camshaft position sensor signals to determine engine speed and ignition timing (coil dwell).

If the PCM does not receive the crankshaft position sensor and camshaft position sensor signals when the ignition switch is in the Run position, it will de-energize the ASD relay.

The ASD relay is located in the Power Distribution Center (PDC). The PDC is located on the driver's side inner fender well (Fig. 5). A label on the underside of the PDC cover identifies the relays and fuses in the PDC.