Engine Control Module: Service and Repair

PCM Mounting:

PCM PROM Location:

PCM PROM
Service of the PCM should normally consist of either replacement of the PCM or PROM, not both. If a diagnostic procedure calls for the PCM or PCM PROM to be replaced, the PROM and PCM should be checked first to see if they are the correct parts. The PROM can easily be checked by using Tech 1 parameter "TCM CAL ID". If the part numbers are correct, remove and separate the PCM and the PROM, replace one or the other (whichever is faulty) and reconnect the two.

NOTE: The service PCM will not contain a PROM. The original PROM must be retained to reinstall in the service PCM. Care should be taken when separating the PROM from the PCM so that neither is damaged.

After replacement of a PCM or PROM, clear PCM DTCs and check the vehicle for proper operation. Poor engine performance, surging, loss of cruise control, improper "SERVICE ENGINE SOON" MIL operation no starts, and/or hard starts may be caused by an improperly seated PROM and if the PROM is missing, DTC 52/109 will set and the vehicle will not start.

CAUTION: To prevent internal PCM damage, the ignition must be "OFF" when disconnecting or reconnecting power to the PCM, as when the battery cables, PCM connectors, or fuses are connected or disconnected.

REMOVE OR DISCONNECT
1. Key "OFF."

NOTE: Key must be "OFF" for a minimum of 30 seconds before disconnecting PCM connectors or battery voltage to allow TP sensor/idle learned values, transaxle shift adapt values, transaxle oil life index and cruise control lash/learn to be stored in the EEPROM. Failure to wait 30 seconds may result in EEPROM reset, DTC 80 and transaxle oil life index being reset.

2. Right hand hush panel.
3. PCM mounting clips and PCM.
4. PCM connectors.
5. PROM cover.
6. PROM.
- Use two fingers to push both retaining clips back away from the PROM at the same time. Grasp the PROM at both ends and lift up and out of the PROM connector. Do Not open the PROM. Use of any other PROM removal method may cause damage to the PROM or PROM connector.

INSPECT
1. PROM "broadcast" code for proper calibration.
2. Alignment notches on the PROM.

INSTALL OR CONNECT
1. PROM.

CAUTION: Press only on the ends of the PROM. Small notches in the PROM must be aligned with the small notches in the PROM connector. Press on the ends of the PROM until the retaining clips swing up into the ends of the PROM. Press the clips into the sides of the PROM until they snap in place. Do Not press on the middle of the PROM.

2. PROM cover.
3. PCM connectors.
4. PCM mounting clips and PCM.
5. Right hand hush panel.
6. Start engine.

Engine should start and run. If it does not, verify that the PCM contains the correct PROM, the PCM is properly connected to the harness, and the 10 amp PCM Fuse (I/P Fuse Block), and the 20 amp PCMfVATS Fuse (left rear power center) are present and not blown.

7. Install Tech 1.
- DTCs 52 and 109 should appear. Clear PCM DTCs.
- PCM DATA should be accessible. If PCM DATA is not accessible or a "NO DATA" message is displayed, verify that the PCM contains the correct PROM, the PCM is properly connected to the harness, and the 10 amp PCM Fuse (I/P Fuse Block) and the 20 amp PCM/VATS Fuse (left rear power center) are present and not blown.

FUNCTIONAL CHECK
1. Start engine and run for one minute.
2. Scan for DTCs using the Tech 1. If DTC 51, or DTC 108 occurs, or if the MIL (Service Engine Soon) is "ON" constantly with no diagnostic trouble codes, the PROM is not fully seated or is defective.

- If not fully seated, press inward on clips on sides of PROM until they snap into place.
- If it is necessary to remove the PROM, follow the previous removal instructions.