Grand Cherokee 2WD V6-3.7L (2008)
Ignition Shut Down Relay (For Antitheft): Description and Operation
The ASD relay supplies battery voltage (12+ volts) to the fuel injectors and ignition coil(s). With certain emissions packages it also supplies 12-volts to
the oxygen sensor heating elements.
The ground circuit for the coil within the ASD relay is controlled by the Powertrain Control Module (PCM). The PCM operates the ASD relay by
switching its ground circuit on and off.
The ASD relay will be shut-down, meaning the 12-volt power supply to the ASD relay will be de-activated by the PCM if:
The ignition key is left in the ON position. This is if the engine has not been running for approximately 1.8 seconds.
There is a crankshaft position sensor signal to the PCM that is lower than pre-determined values.
ASD Sense - PCM Input
ASD SENSE - PCM INPUT
A 12 volt signal at this input indicates to the PCM that the ASD has been activated. The relay is used to connect the oxygen sensor heater element,
ignition coil and fuel injectors to 12 volt + power supply.
This input is used only to sense that the ASD relay is energized. If the Powertrain Control Module (PCM) does not see 12 volts at this input when the
ASD should be activated, it will set a Diagnostic Trouble Code (DTC).