The Powertrain Control Module (PCM) is an electronic device which monitors various input sensors within its control program. The PCM can then process a variety of transmission output functions and devices.

The PCM gathers data from the following electrical sensors, switches and solenoids:

The PCM controls various transmission functions including the following:

The PCM is located underneath the hood on the left inner fender well.

The 1999 model year PCMs have an internal FLASH EEPROM that is non-removable. This FLASH EEPROM must be programmed when you replace the PCM. For complete FLASH EEPROM programming procedures and service precautions, refer to Powertrain Control Module Replacement in Engine Controls.

The Powertrain Control Module (PCM) is equipped with a self diagnostic feature that detects system failures and aids the technician in locating a faulty circuit. The PCM has memory for comparing various input information to programmed information. These conditions are described on the support page for each Diagnostic Trouble Code (DTC). If a value is not within the PCM parameters, a DTC will set and the default values or actions will be used, if applicable.

The PCM continually performs a self diagnostic check. You can use a scan tool in order to request the PCM to display any stored DTC. You cannot flash the DTC by grounding the DLC.

Important:  Refer to Strategy Based Diagnosis in General Information, before beginning any diagnosis.

Important: Always refer to Powertrain On Board Diagnostic (OBD) System Check in Engine Controls, before diagnosing any DTC.

The scan tool displays all stored DTCs and Freeze Frame or Failure Records in current and history status. If the DTC is in history status, the problem may be intermittent. An intermittent DTC is one which will not reset during the current ignition cycle. The support page of a DTC contains Diagnostic Aids to help locate intermittent conditions.

When diagnosing specific DTCs, always diagnose and repair the first DTC set. After you have made the repair and the DTC is cleared, road test the vehicle and check for DTCs to reset. A failed component or circuit often causes other related components and circuits to display faulty information or to set a false DTC.

Each DTC has a specific diagnostic table and support page. The diagnostic table contains a series of tests that pinpoint a specific failure. The support page contains a circuit description, a list of enable conditions that must be met to set the code, a Diagnostic Aids section to help locate intermittent conditions, and a test description section that identifies specific steps in the DTC table. The table and the support page were designed to be used together so that you will better understand the circuit and the diagnostic procedure.

If a visual check does not locate the cause of the fault, test the suspected circuit withJ 39200 digital multimeter (DMM). Use J 39200 DMM to check for the following opens and shorts:

For a complete test description and procedure, refer to General Electrical Diagnosis in Wiring Systems.

Intermittent and Performance Diagnostic Trouble Codes

The DTC tables in this section determine if there is a fault within the circuit. The fault must be present in order to locate the problem. If an intermittent condition occurs, a DTC is stored in history status, but a check of the circuit will indicate a normal condition. When diagnosing intermittent trouble codes, thoroughly check the suspected circuit for the following conditions:

Clearing History DTCs

After you have completed the repairs, clear all history DTCs with a scan tool. DTCs clear automatically when the vehicle achieves 40 warm up cycles without a reported failure.

PCM Reprogramming

For the 1999 model year, controllers will no longer feature a replaceable EPROM. The controller and the EEPROM chips will be removed and replaced as a unit. For the complete reprogramming procedure, refer to Powertrain Control Module Replacement in Engine Controls.