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.

CIRCUIT OPERATION
Circuit A0 from the bus bar in the Power Distribution Center (PDC) supplies battery voltage to the coil side of the Automatic Shut Down (ASD) relay. The Powertrain Control Module (PCM) controls the relay by supplying ground for the coil side on circuit K51. Circuit K51 connects to cavity 67 of the PCM.

When the PCM grounds the ASD relay, contacts inside the relay CLOSE and connect circuit #4 from fuse 12 in the PDC to circuit A142. Circuit A142 supplies battery voltage to the generator field, ignition coils, fuel injectors, and the heater elements in the heated oxygen sensors. Circuit A142 also connects to cavity 6 of the PCM.