Jeep Grand Cherokee WK. Manual — part 357
OPERATION
POWERTRAIN CONTROL MODULE (PCM)
The PCM is a pre-programmed, microprocessor digital computer. It regulates ignition timing, air-fuel ratio, emission
control devices, charging system, certain transmission features, speed control, air conditioning compressor clutch
engagement and idle speed. The PCM can adapt its programming to meet changing operating conditions.
The PCM receives input signals from various switches and sensors. Based on these inputs, the PCM regulates
various engine and vehicle operations through different system components. These components are referred to as
Powertrain Control Module (PCM) Outputs. The sensors and switches that provide inputs to the PCM are consid-
ered Powertrain Control Module (PCM) Inputs.
The PCM adjusts ignition timing based upon inputs it receives from sensors that react to: engine rpm, manifold
absolute pressure, engine coolant temperature, throttle position, transmission gear selection (automatic transmis-
sion), vehicle speed and the brake switch.
The PCM adjusts idle speed based on inputs it receives from sensors that react to: throttle position, vehicle speed,
transmission gear selection, engine coolant temperature and from inputs it receives from the air conditioning clutch
switch and brake switch.
Based on inputs that it receives, the PCM adjusts ignition coil dwell. The PCM also adjusts the generator charge
rate through control of the generator field and provides speed control operation.
NOTE: PCM Inputs:
•
Accelerator pedal position sensor (if equipped)
•
A/C request (if equipped with factory A/C)
•
A/C select (if equipped with factory A/C)
•
Auto shutdown (ASD) sense
•
Battery temperature
•
Battery voltage
•
Brake switch
•
CAN bus (+) circuits
•
CAN bus (-) circuits
•
Camshaft position sensor signal
•
Clutch Interlock Switch (if equipped)
•
Crankshaft position sensor
•
Data link connection for diagnostic scan tool
•
EGR position sensor (if equipped)
•
Engine coolant temperature sensor
•
Fuel level
•
Generator (battery voltage) output
•
Ignition circuit sense (ignition switch in on/off/crank/run position)
•
Intake manifold air temperature sensor
•
Knock sensor(s) (if equipped)
•
Leak detection pump (switch) sense (if equipped)
•
Manifold absolute pressure (MAP) sensor
•
Oil pressure sensor
•
Output shaft speed sensor
•
Overdrive/override switch
•
Oxygen sensors
•
Park/neutral switch (auto. trans. only)
•
Power ground
•
Power steering pressure switch (if equipped)
•
Sensor return
•
Signal ground
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•
Speed control multiplexed single wire input
•
Throttle position sensor
•
Transmission governor pressure sensor
•
Transmission output speed sensor
•
Transmission temperature sensor
•
Vehicle speed inputs from ABS or RWAL system
NOTE: PCM Outputs:
•
A/C clutch relay
•
Auto shutdown (ASD) relay
•
CAN bus (+/-) circuits for: speedometer, voltmeter, fuel gauge, oil pressure gauge/lamp, engine temp. gauge
and speed control warn. lamp
•
Data link connection for diagnostic scan tool
•
Double start override (if equipped)
•
EGR valve control solenoid (if equipped)
•
Electronic throttle control
•
EVAP canister purge solenoid
•
Five volt sensor supply (primary)
•
Five volt sensor supply (secondary)
•
Fuel injectors
•
Fuel pump relay
•
Generator field driver (-)
•
Generator field driver (+)
•
Generator lamp (if equipped)
•
Idle air control (IAC) motor
•
Ignition coil(s)
•
CAN bus circuits
•
Leak detection pump (if equipped)
•
Malfunction indicator lamp (Check engine lamp). Driven through CAN bus circuits.
•
Overdrive indicator lamp (if equipped)
•
Radiator cooling fan (if equipped)
•
Speed control vacuum solenoid
•
Speed control vent solenoid
•
Starter relay
•
Tachometer (if equipped). Driven through CAN bus circuits.
•
Transmission convertor clutch circuit
•
Transmission 3-4 shift solenoid
•
Transmission relay
•
Transmission temperature lamp (if equipped)
•
Transmission variable force solenoid
5 VOLT SUPPLIES
Primary 5–volt supply:
•
supplies the required 5 volt power source to the Crankshaft Position (CKP) sensor.
•
supplies the required 5 volt power source to the Camshaft Position (CMP) sensor.
•
supplies a reference voltage for the Manifold Absolute Pressure (MAP) sensor.
•
supplies a reference voltage for the Throttle Position Sensor (TPS) sensor.
Secondary 5–volt supply:
•
supplies the required 5 volt power source to the oil pressure sensor.
•
supplies the required 5 volt power source for the Vehicle Speed Sensor (VSS) (if equipped).
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•
supplies the 5 volt power source to the transmission pressure sensor (if equipped with an RE automatic trans-
mission).
IGNITION CIRCUIT SENSE
The ignition circuit sense input tells the PCM the ignition switch has energized the ignition circuit.
Battery voltage is also supplied to the PCM through the ignition switch when the ignition is in the RUN or START
position. This is referred to as the
9
ignition sense
9
circuit and is used to
9
wake up
9
the PCM. Voltage on the ignition
input can be as low as 6 volts and the PCM will still function. Voltage is supplied to this circuit to power the PCM’s
8-volt regulator and to allow the PCM to perform fuel, ignition and emissions control functions.
REMOVAL
CAUTION: Certain ABS systems rely on having the Powertrain Control Module (PCM) broadcast the Vehicle
Identification Number (VIN) over the bus network. To prevent problems of DTCs and other items related to
the VIN broadcast, it is recommend that you disconnect the ABS CAB (controller) temporarily when replac-
ing the PCM. Once the PCM is replaced, write the VIN to the PCM using a diagnostic scan tool. This is done
from the engine main menu. Arrow over to the second page to “1. Miscellaneous”. Select “Check VIN” from
the choices. Make sure it has the correct VIN entered before continuing. When the VIN is complete, turn off
the ignition key and reconnect the ABS module connector. This will prevent the setting of DTCs and other
items associated with the lack of a VIN detected when you turn the key ON after replacing the PCM.
CAUTION: Use a diagnostic scan tool to reprogram the new PCM with the vehicles original identification
number (VIN) and the vehicles original mileage. If this step is not done, a Diagnostic Trouble Code (DTC)
may be set.
The PCM (1) is attached to the right-front inner fender located in the engine compartment.
To avoid possible voltage spike damage to the PCM, ignition key must be off, and negative battery cable must be
disconnected before unplugging PCM connectors.
1. Disconnect and isolate negative battery cable.
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2. Carefully unplug the 38-way connectors (2) from PCM.
3. A locating pin (5) is used in place of one of the PCM mounting bolts. Pry clip (4) from pin (5).
4. Remove two PCM mounting bolts (2), and remove PCM from vehicle.
5. Position ground strap (3) to the side.
INSTALLATION
CAUTION: Certain ABS systems rely on having the Powertrain Control Module (PCM) broadcast the Vehicle
Identification Number (VIN) over the bus network. To prevent problems of DTCs and other items related to
the VIN broadcast, it is recommend that you disconnect the ABS CAB (controller) temporarily when replac-
ing the PCM. Once the PCM is replaced, write the VIN to the PCM using a diagnostic scan tool. This is done
from the engine main menu. Arrow over to the second page to “1. Miscellaneous”. Select “Check VIN” from
the choices. Make sure it has the correct VIN entered before continuing. When the VIN is complete, turn off
the ignition key and reconnect the ABS module connector. This will prevent the setting of DTCs and other
items associated with the lack of a VIN detected when you turn the key ON after replacing the PCM.
CAUTION: Use a diagnostic scan tool to reprogram the new PCM with the vehicles original identification
number (VIN) and the vehicles original mileage. If this step is not done, a Diagnostic Trouble Code (DTC)
may be set.
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