Grand Cherokee 2WD L6-4.0L VIN S (1997)
Powertrain Control Module: Description and Operation
Battery Feed
CIRCUIT OPERATION
Circuit F5 from fuse 20 in the Power Distribution Center (PDC) supplies battery voltage to cavity A22 of the Powertrain Control Module (PCM).
Ground
CIRCUIT OPERATION
Circuit Z12 connects to cavities A31 and A32 of the PCM. The Z12 circuit provides ground for PCM internal drivers that operate high current
devices like the injectors and ignition coil.
Internal to the PCM, the ground circuit connects to the PCM sensor return circuit (from circuit K4).
Air Conditioning (A/C) Controls
AIR CONDITIONING (A/C) CONTROLS-PCM INPUT
The A/C control system information applies to factory installed air conditioning units.
A/C SELECT SIGNAL:
When the A/C switch is in the ON position, an input signal is sent to the Powertrain Control Module (PCM). The signal informs the PCM that the
A/C has been selected. The PCM adjusts idle speed to a pre-programmed rpm through the Idle Air Control (IAC) motor to compensate for
increased engine load.
A/C REQUEST SIGNAL:
Once A/C has been selected, the PCM receives the A/C request signal from the clutch cycling pressure switch. The input indicates that the
evaporator pressure is in the proper range for A/C application. The PCM uses this input to cycle the A/C compressor clutch (through the A/C
relay). It will also determine the correct engine idle speed through the IAC motor position.
If the A/C low-pressure switch or high-pressure switch opens (indicating a low or high refrigerant pressure), the PCM will not receive an A/C
request signal. The PCM will then remove the ground from the A/C relay. This will deactivate the A/C compressor clutch.
If the switch opens, (indicating that evaporator is not in proper pressure range), the PCM will not receive the A/C request signal. The PCM will
then remove the ground from the A/C relay deactivating the A/C compressor clutch.
Automatic Shutdown (ASD) Relay Sense
AUTOMATIC SHUTDOWN (ASD) RELAY SENSE- PCM INPUT
Fig. 2 PDC
A 12 volt signal at this input indicates to the Powertrain Control Module (PCM) that the Automatic Shutdown (ASD) relay 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 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 PCM does not see 12 volts at this input when the ASD should be activated,
