Powertrain Control Module Diagnosis

Because the Powertrain Control Module (PCM) can have a fault which may affect only one circuit, the following diagnostic procedures in this section will determine which circuit has a problem and where it Is.

If a diagnostic table indicates that the PCM connections or PCM is the cause of a problem, and the PCM is replaced, but does not correct the problem, one of the following may be the reason:

^ There is a problem with the PCM terminal connections. - The diagnostic table will say PCM connections or PCM. The terminals may have to be removed from the connector in order to check them properly.

^ The PCM, or EEPROM calibration is not correct for the application. - The incorrect components or calibration may cause a malfunction and may or may not set a DTC.

^ The problem is intermittent. - This means that the problem is not present at the time the system is being checked. In this case, refer to the Intermittents and make a careful physical inspection of all portions of the system involved. - Intermittent Malfunctions

^ Shorted solenoid, relay coil, or harness. - Solenoids and relays are turned ON and OFF by the PCM using internal electronic switches called drivers. Each driver is part of a group of seven called an output driver module or group of four called a quad-driver module. The drivers switch the ground side of a solenoid or relay circuit which is fed by connection to battery voltage. A shorted or low resistance solenoid or relay, or a shorted harness can allow TCC much current to flow through a driver. This will not permanently damage a PCM, as the driver will limit current. However, a circuit which tends to allow TCC much current into the driver will probably cause the solenoid or relay to become inoperative, and can be diagnosed in A/C Compressor Clutch Control Diagnosis for the A/C relay, or Electric Cooling Fan Diagnosis for the cooling fan relay, or PCM Outputs Diagnosis for output driver module outputs. PCM Outputs Diagnosis

^ The EEPROM may be malfunctioning. - Although these rarely fail, it operates as part of the PCM. Therefore, it could be the cause of the problem. A DTC will set if the EEPROM is malfunctioning. Follow any DTC tables for any DTCs that may set.

^ The replacement PCM may be malfunctioning. - After the PCM is replaced, the system should be re-checked for proper operation. Refer to the Powertrain OBD System. Testing and Inspection

If a diagnostic table again indicates the PCM is the problem, re-program or if necessary, substitute a known good PCM. Although this is a rare condition, it is possible.