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Home >> GMC >> 2006 >> Sierra 1500 HD, RWD >> Repair and Diagnosis >> External Pages >> Different car >> Section 981 (Lighting Systems) >> Diagnostic Information and Procedures >> Interior Backlighting Malfunction (w/o AN3) >> Circuit/System Testing

Circuit/System Testing

WARNING: This page is about a different car, the 2008 GMC Sierra, 2008 GMC Cab & Chassis Sierra, 2008 Chevrolet Silverado, and 2008 Chevrolet Cab & Chassis Silverado. However, it is still accessible from the selected car via links, so may be relevant.

Dimmer Switch Circuit Test

  1. Ignition OFF, disconnect the harness connector at the headlamp switch.
  2. Ignition OFF, verify that a test lamp illuminates between the ground circuit terminal 8 and B+.
    • If the test lamp does not illuminate, test the ground circuit for an open/high resistance.
  3. Ignition ON, verify the scan tool Dimming Control Signal parameter is less than 0.1 volts.
    • If greater than the specified range, test the signal circuit terminal 13 for a short to voltage. If the circuit tests normal, replace the BCM.
  4. Ignition ON, test for B+ between the I/P dimming voltage reference circuit terminal 15 and ground.
    • If less than the specified value, test the voltage reference circuit for a short to ground or an open/high resistance. If the circuit tests normal, replace the BCM.
  5. Install a 3A fused jumper wire between the signal circuit terminal 13 and the voltage reference circuit terminal 15. Verify the scan tool BCM Dimming Control Signal parameter is greater than 2.6 volts.
    • If less than the specified range, test the signal circuit for a short to ground or an open/high resistance. If the circuit tests normal, replace the BCM.
  6. If all circuits test normal, test or replace the headlamp switch.

Interior Backlighting Circuit Test

  1. Ignition OFF, disconnect the harness connector at the affected component.
  2. Ignition OFF, verify that a test lamp illuminates between the listed ground circuit terminal and battery voltage.
    • Passenger window switch terminal F
    • Headlamp switch terminal 8
    • Transfer case control switch terminal 6
    • Sunroof switch terminal 5
    • Door lock switch terminal B
    • Roof beacon switch terminal 1
    • Sliding rear window switch terminal D
    • Garage door opener switch terminal 3
    • Outside rear view mirror switch terminal G
    • Driver window switch terminal A X2
    • If the test lamp does not illuminate, test the ground circuit for an open/high resistance.
  3. Connect a test lamp between the listed backlighting control circuit terminal and ground.
    • Passenger window switch terminal B
    • Headlamp switch terminal 7
    • Transfer case control switch terminal 5
    • Sunroof switch terminal 3
    • Door lock switch terminal A
    • Roof beacon switch terminal 2
    • Sliding rear window switch terminal E
    • Garage door opener switch terminal 2
    • Outside rear view mirror switch terminal E
    • Driver window switch terminal 1 X1
  4. Command the dimming test high to low with a scan tool. The test lamp should turn from bright to dim when changing between the commanded states.
    • If the test lamp is always off, test the control circuit for an open/high resistance or short to ground. If the circuit tests normal, replace the BCM.
    • If the test lamp is always bright, test the control circuit for a short to voltage. If the circuit tests normal, replace the BCM.
  5. If all circuits test normal, test or replace the affected component.

LED Dimming Circuit Test

  1. Ignition OFF, disconnect the harness connector at the affected component.
  2. Ignition OFF, verify that a test lamp illuminates between the listed ground circuit terminal and battery voltage.
    • Right steering wheel switch terminal 1
    • Left steering wheel switch terminal 8
    • DIC switch terminal 5
    • Manual HVAC control module terminal 10 X2
    • Multifunction accessory switch terminal 3
    • If the test lamp does not illuminate, test the ground circuit for an open/high resistance.
  3. Connect a test lamp between the listed LED dimming control circuit terminal and ground.
    • Right steering wheel switch terminal 2
    • Left steering wheel switch terminal 6
    • Power take off switch terminal 6
    • Trailer brake controller switch terminal 7
    • IPC terminal 8
    • Radio terminal 7 X1
    • DIC switch terminal 4
    • Manual HVAC control module terminal 1 X2
    • Multifunction accessory switch terminal 4
  4. Command the dimming test high to low with a scan tool. The test lamp should turn from bright to dim when changing between the commanded states.
    • If the test lamp is always off, test the control circuit for an open/high resistance or short to ground. If the circuit tests normal, replace the BCM.
    • If the test lamp is always bright, test the control circuit for a short to voltage. If the circuit tests normal, replace the BCM.
  5. If all circuits test normal, test or replace the affected component.
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