Body Control Module Replacement

BODY CONTROL MODULE REPLACEMENT

REMOVAL PROCEDURE

IMPORTANT:
- The ignition switch should be in the OFF position when connecting or disconnecting the connectors to the body control module (BCM).
- Always disconnect the 40-way body wiring extension FIRST, the 32-way tan connector SECOND and the 24-way gray electrical connector LAST.
- Always connect the 24-way gray electrical connector FIRST, the 32-way tan connector SECOND and the 40-way body wiring extension LAST.
- The BCM can set DTCs with the ignition switch in the OFF position. The BCM has battery run down protection for the courtesy lamp circuit. The BCM battery run down protection cannot detect shorts on inputs or other circuits which the BCM does not control. Use the scan tool in order to activate the POWER DOWN NOW mode. Use the POWER DOWN NOW mode in order to check for current draws on circuits that are not controlled by the BCM, or controlled by the battery run down protection system.
- Do not touch the exposed electrical contacts of the body wiring extension. Do not open the BCM housing. The module does not have any serviceable components. The module may be replaced only as an assembly.

1. Disconnect the negative battery cable.

CAUTION: Unless directed otherwise, the ignition and start switch must be in the OFF or LOCK position, and all electrical loads must be OFF before servicing any electrical component. Disconnect the negative battery cable to prevent an electrical spark should a tool or equipment come in contact with an exposed electrical terminal. Failure to follow these precautions may result in personal injury and/or damage to the vehicle or its components.

For Vehicles equipped with OnStar (RPO UE1) with Back Up Battery:
The Back Up Battery is a redundant power supply to allow limited OnStar functionality in the event of a main vehicle battery power disruption to the VCIM (OnStar module). Do not disconnect the main vehicle battery or remove the OnStar fuse with the ignition key in any position other than OFF. Retained accessory power (RAP) should be allowed to time out or be disabled (simply opening the driver door should disable RAP) before disconnecting power. Disconnecting power to the OnStar module in any way while the ignition is On or with RAP activated may cause activation of the OnStar Back-Up Battery (BUB) system and will discharge and permanently damage the back-up battery. Once the Back-Up Battery is activated it will stay on until it has completely discharged. The BUB is not rechargeable and once activated the BUB must be replaced.

2. If replacing the BCM on a Chevrolet TrailBlazer EXT or GMC Envoy XL, remove the left second row seat.
3. If replacing the BCM on a Chevrolet TrailBlazer or GMC Envoy, position the left hand second seat to a cargo position.




4. Remove the rear electrical center cover.




5. Press down and hold the locking tab (1).
6. Disengage the sliding latch retaining the BCM to the rear electrical center.Slide the latch inboard until fully extended, approximately 40 mm (1.6 in).




7. Disconnect the 40-way body wiring extension (1) from the BCM.




8. Disconnect the 32-way tan electrical connector (2) from the BCM.
9. Disconnect the 24-way gray electrical connector (1) from the BCM.




10. With an upward motion, remove the BCM (1) from the rear electrical center.

INSTALLATION PROCEDURE




1. Index the slots on the BCM (1) to the rear electrical center.
2. Using a downward motion, install the BCM to the rear electrical center.




3. Connect the 24-way gray electrical connector (1) to the BCM.
4. Connect the 32-way tan electrical connector (2) to the BCM.




5. Connect the 40-way body wiring extension (1) to the BCM.




6. Engage the sliding latch fastening the BCM to the rear electrical center. Slide the latch outboard until the locking tab (1) is fully seated.




7. Install the rear electrical center cover.
8. If replacing the BCM on a Chevrolet TrailBlazer or GMC Envoy, position the left hand second seat to a passenger position.
9. If replacing the BCM on a Chevrolet TrailBlazer EXT or GMC Envoy XL, install the left second row seat.
10. Connect the negative battery cable.
11. If installing a replacement BCM, program the BCM. Programming and Relearning