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

Power Distribution Center:

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

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

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

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.

AUTOMATIC SHUTDOWN (ASD) SENSE-PCM INPUT
OPERATION
The ASD sense circuit informs the PCM when the ASD relay energizes. A 12 volt signal at this input indicates to the PCM that the ASD has been activated. This input is used only to sense that the ASD relay is energized.

When energized, the ASD relay supplies battery voltage to the fuel injectors, ignition coils and the heating element in each oxygen sensor. If the PCM does not receive 12 volts from this input after grounding the ASD relay, it sets a Diagnostic Trouble Code (DTC).

AUTOMATIC SHUTDOWN RELAY-PCM OUTPUT
The Automatic Shutdown (ASD) relay supplies battery voltage to the fuel injectors, electronic ignition coil and the heating elements in the oxygen sensors.

A buss bar in the Power Distribution Center (PDC) supplies voltage to the solenoid side and contact side of the relay. The ASD relay power circuit contains a 25 amp fuse between the buss bar in the PDC and the relay. The fuse is located in the PDC.

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 O2 Heater Monitor test is being run. Refer to On-Board Diagnostics. 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.

Power Distribution Center:

The ASD relay is located in the PDC. A label affixed to the underside of the PDC cover identifies the relays and fuses in the PDC.