PT Cruiser, 2001 - 2005

Powertrain Control Module (PCM)


Description & Operation

The Powertrain Control Module (PCM) is a digital computer containing a microprocessor.

The PCM receives input signals from various switches and sensors that are referred to as PCM Inputs. Based on these inputs, the PCM adjusts various engine and vehicle operations through devices that are referred to as PCM Outputs.

PCM Ground

Ground is provided through multiple pins of the PCM connector. Depending on the vehicle there may be as many as three different ground pins. There are power grounds and sensor grounds. The power grounds are used to control the ground side of any relay, solenoid, ignition coil or injector. The signal ground is used for any input that uses sensor return for ground, and the ground side of any internal processing component.

The SBEC III case is shielded to prevent RFI and EMI. The PCM case is grounded and must be firmly attached to a good, clean body ground. Internally all grounds are connected together, however there is noise suppression on the sensor ground. For EMI and RFI protection the case is also grounded separately from the ground pins.

Use the proper 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 engine control strategy prevents reduced idle speeds until after the engine operates for 200 miles If the PCM is replaced after 200 miles of usage, update the mileage and vehicle identification number (VIN) in the new PCM. Use the DRB scan tool to change the mileage and VIN in the PCM. If this step is not done a Diagnostic Trouble Code (DTC) may be set. The PCM attaches to a bracket welded on the dash panel.

PCM Inputs

Air Conditioning Controls
Battery Voltage
Battery Temperature Sensor
Brake Switch
Camshaft Position Sensor
Crankshaft Position Sensor
Engine Coolant Temperature Sensor
Fuel Level Sensor
Ignition Switch
Intake Air Temperature Sensor
Knock Sensor (2.0/2.4L only)
Leak Detection Pump
Manifold Absolute Pressure (MAP) Sensor
Oxygen Sensors
Power Steering Pressure Switch
SCI Receive
Speed Control Switches
Throttle Position Sensor
Transmission Park/Neutral Switch (automatic transmission)
Vehicle Speed Sensor

PCM Outputs

Air Conditioning Clutch Relay
Auto Shutdown (ASD) Relay
Charging Indicator Lamp
SCI Transmit
Proportional Purge Solenoid
EGR Solenoid
Fuel Injectors
Fuel Pump Relay
Generator Field
Idle Air Control Motor
Ignition Coils
Malfunction Indicator (Check Engine) Lamp
Radiator Fan Relays
Speed Control Solenoids

Based on inputs it receives, the PCM adjusts fuel injector pulse width, idle speed, ignition spark advance, ignition coil dwell and EVAP canister purge operation. The PCM regulates the cooling fan, air conditioning and speed control systems. The PCM changes generator charge rate by adjusting the generator field. The PCM also performs diagnostics.

The PCM adjusts injector pulse width (air-fuel ratio) based on the following inputs:

Battery voltage
Coolant temperature
Exhaust gas content (oxygen sensor)
Engine speed (crankshaft position sensor)
Intake air temperature
Manifold absolute pressure
Throttle position

The PCM adjusts ignition timing based on the following inputs:

Coolant temperature
Engine speed (crankshaft position sensor)
Knock sensor
Manifold absolute pressure
Throttle position
Transmission gear selection (park/neutral switch)
Intake air temperature

The PCM also adjusts engine idle speed through the idle air control motor based on the following inputs:

Air conditioning sense
Battery voltage
Battery temperature
Brake switch
Coolant temperature
Engine speed (crankshaft position sensor)
Engine run time
Manifold absolute pressure
Power steering pressure switch
Throttle position
Transmission gear selection (park/neutral switch)
Vehicle distance (speed)

The Auto Shutdown (ASD) and fuel pump relays are located in the Power Distribution Center (PDC).

The camshaft position sensor and crankshaft position sensor signals are sent to the PCM. If the PCM does not receive the signal within approximately 1 second of engine cranking, it deactivates the ASD relay and fuel pump relay. When these relays are deactivated, power is shut off from the fuel injectors, ignition coils, oxygen sensor heating elements and fuel pump.

The PCM contains a voltage converter that changes battery voltage to a regulated 9 volts direct current to power the camshaft position sensor, crankshaft position sensor and vehicle speed sensor. The PCM also provides a 5-volt direct current supply for the manifold absolute pressure sensor, throttle position sensor, and A/C pressure switch.

Removal & Installation

  1. Remove the air cleaner lid, disconnect the inlet air temperature sensor and makeup air hose.
  3. Remove the negative battery cable.
  5. Remove screws attaching PCM to dash panel bracket.
  7. Unlock the connector then disconnect both 40-way connectors from the PCM.
  9. Lift PCM up to remove it from vehicle.

To install:

  1. Install PCM. Tighten mounting screws to 10.7 Nm (95 inch lbs.).
  3. Attach both 40-way connectors to PCM. Lock the tabs.
  5. Install the negative battery cable.
  7. Install the air cleaner lid; connect the inlet air temperature sensor and makeup air hose.

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