LaCrosse 2006-2007

Powertrain Control Module

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Operation



The powertrain has electronic controls to reduce exhaust emissions while maintaining excellent drivability and fuel economy. The Powertrain Control Module (PCM) is the control center of this system. The PCM monitors numerous engine and vehicle functions. The PCM constantly looks at the information from various sensors and other inputs, and controls the systems that affect vehicle performance and emissions. The PCM also performs the diagnostic tests on various parts of the system. The PCM can recognize operational problems and alert the driver via the Malfunction Indicator Lamp (MIL). When the PCM detects a malfunction, the PCM stores a Diagnostic Trouble Code (DTC). The problem area is identified by the particular DTC that is set. The control module supplies a buffered voltage to various sensors and switches. Review the components and wiring diagrams in order to determine which systems are controlled by the PCM. The following are some of the functions that the PCM controls:



The engine fueling
 
The Ignition Control (IC)
 
The Knock Sensor (KS) system
 
The Evaporative Emissions (EVAP) system
 
The Secondary Air Injection (AIR) system (if equipped)
 
The Exhaust Gas Recirculation (EGR) system
 
The automatic transmission functions
 
The alternator
 
The A/C clutch control
 
The cooling fan control
 

Removal & Installation



3.6L Engine

For removal and installation, refer to Electronic Control Module (ECM) which may also be referred to as the Engine Control Module (ECM).

3.8L Engine

NOTE
Service of the Powertrain Control Module (PCM) should normally consist of either replacement of the PCM or Electrically Erasable Programmable Read Only Memory (EEPROM) programming. If the diagnostic procedures call for the PCM to be replaced, the PCM should be inspected first to see if the correct part is being used. If the correct part is being used, remove the faulty PCM and install the new service PCM.


WARNING
Turn the ignition OFF when installing or removing the control module connectors and disconnecting or reconnecting the power to the control module (battery cable, PCM/Engine Control Module (ECM)/Transaxle Control Module (TCM) pigtail, control module fuse, jumper cables, etc.) in order to prevent internal control module damage.


WARNING
Control module damage may result when the metal case contacts battery voltage. DO NOT contact the control module metal case with battery voltage when servicing a control module, using battery booster cables, or when charging the vehicle battery.


WARNING
In order to prevent any possible electrostatic discharge damage to the control module, do no touch the connector pins or the soldered components on the circuit board.


NOTE
Remove any debris from around the control module connector surfaces before servicing the control module. Inspect the control module connector gaskets when diagnosing or replacing the control module. Ensure that the gaskets are installed correctly. The gaskets prevent contaminant intrusion into the control module.


NOTE
The new service PCM will not be programmed. You must program the new PCM. DTC P0602 indicates the EEPROM is not programmed or has malfunctioned.


NOTE
It is necessary to record the remaining engine oil life. If the replacement module is not programmed with the remaining engine oil life, the engine oil life will default to 100 percent. If the replacement module is not programmed with the remaining engine oil life, the engine oil will need to be changed at 3,000 miles (5,000 km) from the last engine oil change.

  1. Using a scan tool, retrieve the percentage of remaining engine oil life. Record the remaining engine oil life.
  2.  
  3. Remove or disconnect the following:

    The negative battery cable
     
    The left front inner fender brace
     
    The air cleaner intake duct
     
    The air cleaner housing cover screws (2)
     
    The air cleaner housing cover (1)
     

  4.  
  5. Without disconnecting the PCM electrical connectors, remove the PCM and the wiring harness from the air cleaner housing assembly (3).
  6.  
  7. Disconnect the PCM electrical connectors and remove the PCM (4).

    Click image to see an enlarged view

    Fig. Powertrain Control Module (PCM) location-3.8L engine

  8.  

To install:

  1. Install or connect the following:

    The PCM to the PCM electrical connectors (4). Tighten the connectors to 71 inch lbs. (8 Nm)
     
    The PCM and the wiring harness to the air cleaner housing assembly (3)
     
    The air cleaner housing cover (1)
     
    The air cleaner housing cover screws (2). Tighten the screws to 35 inch lbs. (4 Nm)
     
    The air cleaner intake duct
     
    The left front inner fender brace
     
    The negative battery cable
     

  2.  
  3. If a new PCM is being installed, the PCM must be programmed.
  4.  

Testing



The Powertrain Control Module (PCM) is programmed with test routines that test the operation of the various systems the PCM controls. Some tests monitor internal PCM functions. Many tests are run continuously. Other tests run only under specific conditions, referred to as conditions for running the DTC. When the vehicle is operating within the conditions for running a particular test, the PCM monitors certain parameters and determines if the values are within an expected range. The parameters and values considered outside the range of normal operation are listed as conditions for setting the DTC. When the conditions for setting the DTC occur, the PCM executes the action taken when the DTC Sets. Some DTC-s alert the driver via the Malfunction Indicator Lamp (MIL) or a message. Other DTC-s do not trigger a driver warning, but are stored in memory. The PCM also saves data and input parameters when most DTC-s are set. This data is stored in the freeze frame and/or failure records.

The DTC-s are categorized by type. The DTC type is determined by the MIL operation and the manner in which the fault data is stored when a particular DTC fails. In some cases there may be exceptions to this structure. Therefore, when diagnosing the system it is important to read the action taken when the DTC sets and the conditions for clearing the DTC.

Many intermittent open or shorted circuits come and go with harness and connector movement caused by vibration, engine torque, bumps, and rough pavement.

  1. Test the wiring harness and connectors by performing the following:

    Move the related PCM connectors and wiring while monitoring the appropriate scan tool data
     
    With the engine running, move the related connectors and wiring while monitoring engine operation
     
    If harness or connector movement affects the data displayed, the component and system operation, or the engine operation, inspect and repair the harness or connections as necessary
     

  2.  
  3. Test the electrical connections and/or wiring by performing the following:

    Inspect for incorrect mating of the connector halves, or terminals not fully seated in the connector body, backed-out
     
    Inspect for improperly formed or damaged terminals. Test for incorrect terminal tension
     
    Inspect for poor terminal to wire connections including terminals crimped over insulation. This requires removing the terminal from the connector body
     
    Inspect for corrosion or water intrusion. Pierced or damaged insulation can allow moisture to enter the wiring. The conductor can corrode inside the insulation with little visible evidence. Look for swollen and stiff sections of wire in the suspect circuits
     
    Inspect for wires that are broken inside the insulation
     

  4.  

 
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