Important: Both the vehicle interface unit (VIU) and the vehicle communication unit (VCU) have a specific set of unique numbers that tie the module to the vehicle where the module resides. These numbers, the 10-digit station identification and the 11-digit electronic serial number, are used by the National Cellular Network and OnStar® to identify the specific vehicle. Because these numbers are tied to the vehicle identification number (VIN) of the vehicle, do NOT exchange these parts with those of another vehicle.

1. Remove the rear compartment trim. Refer to Rear Compartment Trim Panel Replacement .
2. Disconnect the electrical connectors on the VIU module.
3. Remove the global position sensor (GPS) antenna cable (2) from the VIU module.
4. Remove the VIU module from the bracket assembly.
5. The old VIU must be returned for core credit.

1. Record the 10-digit STID number from the label on the new module.



2. Install the VIU module onto the bracket assembly.
3. Reconnect the electrical connectors.
4. Connect the GPS antenna cable (2) to the VIU.

Important: After replacing the VIU, you must reconfigure the OnStar® system. Failure to reconfigure the system will result in an additional customer visit for repair.

5. Reconfigure the OnStar® system. Refer to OnStar Reconfiguration .
6. Install the rear compartment trim. Refer to Rear Compartment Trim Panel Replacement .