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Diagnostic Procedures

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.
  1. If BCM diagnostic system check has been performed, go to next step. If BCM diagnostic system check has not been performed, perform BCM diagnostic system check. See BCM DIAGNOSTIC SYSTEM CHECK  under SYSTEM TESTS.
  2. Ensure headlight and panel dimmer are in AUTO mode, or TBC fuse may blow and damage switch. Turn ignition off. Disconnect Blue BCM connector C2 and remove connector combs. Using test light connected to battery voltage, backprobe Blue BCM connector C2 terminal A11 (White wire). See Figure . If test light illuminates, go to next step. If test light does not illuminate, go to step  6 .
  3. With test light still connected between battery voltage and Blue BCM connector C2 terminal A11, remove Automatic Headlight (AHL) relay from Underhood Bussed Electrical Center (UBEC). See COMPONENT LOCATIONS  . If test light illuminates, go to next step. If test light does not illuminate, go to step  5 .
  4. Repair short to ground in White wire between Blue BCM connector C2 terminal A11 and headlight and panel dimmer switch connector terminal "C". See WIRING DIAGRAMS  . After repair, go to step  7 .
  5. Replace AHL relay. After replacing AHL relay, go to step  7 .
  6. Replace BCM and program. See BODY CONTROL MODULE (BCM)  under REMOVAL & INSTALLATION.
  7. Reconnect all components. Clear DTCs. See CLEARING DIAGNOSTIC TROUBLE CODES (DTCS)  under SELF-DIAGNOSTIC SYSTEM.
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