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BCM Diagnostic System Check

WARNING: This page is about a different car, the 1999 GMC Sierra and 1999 Chevrolet Silverado. However, it is still accessible from the selected car via links, so may be relevant.
NOTE: Use this system check as starting point for any BCM complaint. Most malfunctions are caused by faulty wiring, connectors or components. Use of Tech 2 scan tool is recommended. Follow scan tool manufacturer's instructions.
  1. Turn ignition off. Connect scan tool. Turn ignition on, but DO NOT start engine. Using scan tool, attempt to establish communication with BCM. If scan tool communicates with BCM, go to next step. If scan tool does not communicate with BCM, go to SCAN TOOL DOES NOT COMMUNICATE WITH CLASS 2 SERIAL DATA LINE  .
  2. Using scan tool, select BODY from SYSTEM SELECTION MENU. Select BODY CONTROL MODULE (BCM). If scan tool communicates with BCM, go to next step. If scan tool does not communicate with BCM, BCM option will not be available. Go to step  4 .
  3. Using scan tool, select current DTCs. If no DTCs are stored, repair vehicle by symptom. If any DTCs are stored, perform appropriate test under DIAGNOSTIC TESTS. See BCM DTC DEFINITIONS  table under SELF-DIAGNOSTIC SYSTEM.
  4. Attempt to establish communication with other modules on Class 2 serial data line (IPC, PCM and VCM). If scan tool communicates with other modules, go to next step. If scan tool does not communicate with other modules, go to step  9 .
  5. Check TBC power feed fuse (10-amp) in Underhood Bussed Electrical Center (UBEC). See COMPONENT LOCATIONS  and WIRING DIAGRAMS  . If fuse is blown, go to next step. If fuse is okay, go to step  7 .
  6. Turn headlight and panel dimmer switch to AUTO position. Replace TBC fuse. If TBC fuse blows, go to step  11 . If TBC fuse is okay, go to step  2 .
  7. Using a test light connected to ground, probe both sides of TBC fuse. If test light does not illuminate on both circuits, go to step  12 . If test light illuminates on both circuits, go to next step.
  8. Turn ignition off. Disconnect Brown BCM connector C1 and remove connector combs. Using a test light connected to ground, backprobe Brown BCM connector C1 terminal A2 (Orange wire). See Fig 1 . If test light illuminates, go to next step. If test light does not illuminate, go to step  13 .
  9. Using test light connected to battery voltage, backprobe Brown BCM connector C1 terminals A1 (Black wire) and B1 (Black wire). If test light does not illuminate on both circuits, go to next step. If test light illuminates on both circuits, go to SCAN TOOL DOES NOT COMMUNICATE WITH CLASS 2 SERIAL DATA LINE  .
  10. Repair open in Black wire between ground connection G203 and BCM connector C1 terminal A1 or B1. See WIRING DIAGRAMS  . After repair, go to step  14 .
  11. Repair short to ground in Orange wire between BCM connector C1 terminal A2 and TBC fuse. See WIRING DIAGRAMS  . Replace TBC fuse and go to step  14 .
  12. Replace Underhood Bussed Electrical Center (UBEC). After repair, go to step  14 .
  13. Repair open in Orange wire between BCM connector C1 terminal A2 and TBC fuse. See WIRING DIAGRAMS  . After repair, go to next step.
  14. Reconnect all disconnected components. Using scan tool, clear all DTCs.
Fig 1: Identifying BCM Connector C1 Terminals
G99B02306Courtesy of GENERAL MOTORS CORP.
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