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

Power Distribution Center (PDC):

8W-10-2:

AUTOMATIC SHUTDOWN RELAY
The relay is located in the Power Distribution Center (PDC). For the location of the relay within the PDC, refer to the PDC cover for location. Check electrical terminals for corrosion and repair as necessary.

The Automatic Shutdown (ASD) relay supplies battery voltage to the fuel injectors, generator field, electronic ignition coil and the heating elements in the oxygen sensors.

The PCM controls the ASD 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. When the ignition switch is in ON or Start, the PCM momentarily turns on the ASD relay. While the relay is on the PCM monitors the crankshaft and camshaft position sensor signals to determine engine speed and ignition timing (coil dwell). If the PCM does not receive crankshaft 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
It is an input to the Powertrain Control Module from the rely in the Power Distribution Center, refer to the cover for relay location.

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 provides power to operate the injectors, ignition coil, generator field, O2 sensor heaters (both upstream and downstream), and also provides a sense circuit to the PCM for diagnostic purposes. The PCM energizes the ASD any time there is a Crankshaft Position sensor signal that exceeds a predetermined value. The ASD relay can also be energized after the engine has been turned OFF to perform an O2 sensor heater test, if vehicle is equipped with OBD II diagnostics.

With SBEC III, the ASD relay's electromagnet is fed battery voltage, not ignition voltage. The PCM still provides the ground. As mentioned earlier, the PCM energizes the ASD relay during an O2 sensor heater test. This test is performed only after the engine has been shut OFF. The PCM still operates internally to perform several checks, including monitoring the O2 sensor heaters. This and other DTC tests are explained in detail in the On-Board Diagnostic Student Reference Book.

AUTOMATIC SHUTDOWN RELAY - PCM OUTPUT
The ASD relay is located in the PDC with all the other relays. A decal on the inside of the PDC covers shows the locations of each relay and fuse contained in the PDC.

The Automatic Shutdown (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 O2 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.