Main Relay (Computer/Fuel System): Description and Operation
AUTOMATIC SHUTDOWN (ASD) RELAY SENSE-PCM INPUTPower Distribution Center:
A 12 volt signal at this input indicates to the powertrain control module (PCM) that the ASD has been activated. The ASD relay is located in the Power Distribution Center (PDC). The PDC is located in the engine compartment. Refer to label on PDC cover for relay location. The ASD relay is used to connect the oxygen sensor heater elements, ignition coil, and fuel injectors to the 12 volt + power supply. Jeep models of previous years had used the ASD relay to apply the 12 volt + power supply to the generator field source (+) circuit. This generator circuit is now supplied 12 volts + directly from the PCM.
This input is used Only to sense that the ASD relay is energized. If the PCM does not see 12 volts at this input when the ASD should be activated, it will set a Diagnostic Trouble Code (DTC).
AUTO SHUTDOWN (ASD) RELAY-PCM OUTPUT
The ASD relay is located in the Power Distribution Center (PDC).
The ASD supplies battery voltage to the fuel injectors, ignition coil and oxygen (O2S) sensor beating elements. The ground circuit for the coil in the ASD relay is controlled by the powertrain control module (PCM). The PCM operates the relay by switching the ground circuit on and off.
SYSTEM OPERATION
As one of its functions, the ASD relay will supply battery voltage to the ignition coil. The ground circuit for the ASD relay is controlled by the Powertrain Control Module (PCM). The PCM regulates ASD relay operation by switching the ground circuit on-and-off.