300M V6-3.5L VIN G (2000)
Auto Shut Down (ASD) Relay: Description and Operation
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 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).
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 SHUT DOWN (ASD) AND FUEL PUMP RELAYS - PCM OUTPUT
The ASD relay and fuel pump relay are located in the Power Distribution Center (PDC) near the battery. A decal on the inside of the PDC covers
shows the locations of each relay and fuse contained in the PDC.
The PCM operates the Automatic Shut Down (ASD) relay and fuel pump relay through one ground path. The PCM operates them by switching the
ground path for the relays on and off. Both relays turn on and off at the same time.
The ASD relay connects battery voltage to the fuel injectors and ignition coil. The fuel pump relay connects battery voltage to the fuel pump.
The PCM turns the ground path off when the ignition switch is in the Off position. Both relays are off. 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. If the PCM does
not receive a crankshaft position sensor signal and camshaft position sensor signal when the ignition switch is in the Run position, it de-energizes
both relays. When the relays are de-energized, battery voltage is not supplied to the fuel injectors, ignition coil and fuel pump.
