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Home >> Hummer >> 2008 >> H3 Base, Automatic >> Repair and Diagnosis >> External Pages >> Different car >> Section 172 (Lighting Systems) >> Diagnostic Information and Procedures >> Interior Backlighting Malfunction >> Circuit/System Testing

Circuit/System Testing

WARNING: This page is about a different car, the 2008 Cadillac STS. However, it is still accessible from the selected car via links, so may be relevant.

Dimmer Switch Malfunction

  1. Ignition OFF, disconnect the harness connector at the I/P Dimmer switch.
  2. Ignition OFF, verify that a test lamp illuminates between B+ and the low reference circuit terminal 1.
    • If the test lamp does not illuminate, test the low reference circuit for an open/high resistance.
  3. Ignition ON, verify the scan tool dimming POT A/D parameter is greater than 140 counts.
    • If less than the specified range, test the signal circuit terminal 2 for a short to ground. If the circuit tests normal, replace the IPM.
  4. Install a 3-A fused jumper wire between the signal circuit terminal 2 and the low reference circuit terminal 1. Verify the scan tool dimming POT A/D parameter is less than 30 counts.
    • If greater than the specified range, test the signal circuit for a short to voltage or an open/high resistance. If the circuit tests normal, replace the IPM.
  5. If all circuits test normal, test or replace the I/P dimmer switch.

Interior Backlighting Malfunction - Incandescent

  1. Ignition OFF, disconnect the X1 harness connector at the IPM.
  2. Ignition ON, park lamps ON, verify that a test lamp illuminates between the park lamp voltage supply circuit terminal 1 and ground.
    • If the test lamp does not illuminate, test the voltage supply circuit for a short to ground or an open/high resistance.
  3. Ignition ON, park lamps OFF, verify that a test lamp does not illuminate between the park lamp voltage supply circuit terminal 1 and ground.
    • If the test lamp illuminates, test the voltage supply circuit for a short to voltage.
  4. Ignition OFF, disconnect the harness connector at the component with the inoperative backlighting.
  5. Ignition OFF, verify that a test lamp illuminates between B+ and the ground circuit.
    • If the test lamp does not illuminate, test the ground circuit for an open/high resistance.
  6. Connect a test lamp between the backlight lamp control circuit and ground.
  7. Command the incandescent dimming control ON and OFF with a scan tool. The test lamp should turn ON and OFF when changing between the commanded states.
    • If the test lamp is always OFF, test the control circuit for a short to ground or an open/high resistance. If the circuit tests normal, replace the IPM
    • If the test lamp is always ON, test the control circuit for a short to voltage. If the circuit tests normal, replace the IPM.
  8. If all circuits test normal, test or replace the component with the inoperative incandescent backlighting.

Interior Backlighting Malfunction - LED

  1. Ignition OFF, disconnect the harness connector at the component with the inoperative LED backlighting.
  2. Ignition OFF, verify that a test lamp illuminates between B+ and the ground circuit.
    • If the test lamp does not illuminate, test the ground circuit for an open/high resistance.
  3. Connect a test lamp between the LED dimming control circuit and ground.
  4. Command the LED dimming control ON and OFF with a scan tool. The test lamp should turn ON and OFF when changing between the commanded states.
    • If the test lamp is always OFF, test the control circuit for a short to ground or an open/high resistance. If the circuit tests normal, replace the HVAC control module.
    • If the test lamp is always ON, test the control circuit for a short to voltage. If the circuit tests normal, replace the HVAC control module.
  5. If all circuits test normal, test or replace the component with the inoperative LED backlighting.

Door Switch/Rear Compartment Release Switch Indicator Malfunction

  1. Ignition OFF, disconnect the harness connector at the component with the inoperative backlighting.
  2. Ignition OFF, verify that a test lamp illuminates between B+ and the ground circuit.
    • If the test lamp does not illuminate, test the ground circuit for an open/high resistance.
  3. Connect a test lamp between the backlight lamp control circuit and ground.
  4. Command the appropriate door module door switch backlighting ON and OFF with a scan tool. The test lamp should turn ON and OFF when changing between the commanded states.
    • If the test lamp is always OFF, test the control circuit for a short to ground or an open/high resistance. If the circuit tests normal, replace the appropriate door control module.
    • If the test lamp is always ON, test the control circuit for a short to voltage. If the circuit tests normal, replace the appropriate door control module.
  5. If all circuits test normal, test or replace the component with the inoperative backlighting.
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