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:
Removal & Installation
- Using a scan tool, retrieve the percentage of remaining engine oil life. Record the remaining engine oil life.
Disconnect the negative battery cable.
- Disconnect the 3 Powertrain Control Module (PCM) harness connectors from the PCM, noting proper orientation.
- Use the retaining tab to release the PCM from the underhood junction block bracket.
- Use the retaining tab to secure the PCM, when installing the PCM to the underhood junction block bracket.
- Connect the PCM harness connectors to the PCM.
- Connect the negative battery cable.
- If a new PCM is being installed, the PCM must be programmed.
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 in the supporting text.
Many intermittent open or shorted circuits come and go with harness and connector movement caused by vibration, engine torque, bumps, and rough pavement.
Test the wiring harness and connectors by performing the following:
Move the related PCM connectors and wiring while monitoring the appropriate scan tool data
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