Automatic Shut Down Relay

Fig. 25 Power Distribution Center (PDC):

PURPOSE
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. Refer to Diagrams/Electrical for circuit information.

The Automatic Shutdown (ASD) sense circuit informs the PCM when the ASD relay energizes. 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.

OPERATION
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.

The PCM also monitors the ASD relay output voltage. If the PCM does not receive 12 volts from this input after grounding the ASD relay, it sets a diagnostic trouble code.

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.

The ASD relay is located in the PDC Fig. 25. The inside top of the PDC cover has label showing relay and fuse identification.

Fig. 1 ASD And Fuel Pump Relay Terminals:

CIRCUIT OPERATION
Terminal number 30 is connected to battery voltage. For both the ASD and fuel pump relays, terminal 30 is connected to battery voltage at all times.

The PCM grounds the coil side of the relay through terminal number 85.

Terminal number 86 supplies voltage to the coil side of the relay.

When the PCM de-energizes the ASD and fuel pump relays, terminal number 87A connects to terminal 30. This is the Off position. In the off position, voltage is not supplied to the rest of the circuit. Terminal 87A is the center terminal on the relay.

When the PCM energizes the ASD and fuel pump relays, terminal 87 connects to terminal 30. This is the On position. Terminal 87 supplies voltage to the rest of the circuit.

Power for the coil and contact side of the relay is provided by circuit A14. This circuit is HOT at all times and protected by a 20 amp fuse located in cavity 5 of the PDC.

The Powertrain Control Module (PCM) controls the ground path for the relay on circuit K51. This circuit connects to cavity 67 of the PCM connector.

When the relay is energized, the contacts internal to the relay close connecting circuits A14 and A142. The A142 circuit is spliced and provides power to the fuel injectors, generator, electronic EGR transducer solenoid, and the ignition coil.

The A142 circuit is also spliced and connects to the PCM connector, cavity 6. This input is used for ASD sense by the PCM.

HELPFUL INFORMATION
Check the 20 amp fuse located in cavity 5 of the PDC.