Body Control Module (BCM) Diagnostic System Check

CAUTION: BCM Brown 24-pin connector C1 contains power and ground sources. When removing BCM, always disconnect connector C1 first before disconnecting connectors C2 and C3. When installing BCM, always reconnect connectors C2 and C3, then connector C1 last.

1. Install scan tool. If scan tool works, go to next step. If scan tool does not work, go to SCAN TOOL INOPERATIVE  .
2. Turn ignition on. Attempt to communicate with BCM. If BCM communicates with scan tool, go to next step. If BCM does not communicate with scan tool, go to SCAN TOOL DOES NOT COMMUNICATE WITH CLASS 2 DEVICE  .
3. Check BCM DTCs. If any "U" prefix codes exist, go to SCAN TOOL DOES NOT COMMUNICATE WITH CLASS 2 DEVICE  . If no "U" prefix codes exist, go to DIAGNOSTIC TROUBLE CODE DEFINITIONS  table.

Fig 1: Identifying BCM Connector C1 Terminals

Courtesy of GENERAL MOTORS CORP.

Fig 2: Identifying BCM Connector C2 Terminals

Courtesy of GENERAL MOTORS CORP.

Fig 3: Identifying BCM Connector C3 Terminals

Courtesy of GENERAL MOTORS CORP.