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Home >> Hummer >> 2008 >> H2 4D Utility Wagon >> Repair and Diagnosis >> External Pages >> Different car >> Section 439 (Lighting System) >> Diagnostic Information and Procedures >> Headlamps Malfunction (With T4Q) >> Circuit/System Testing

Circuit/System Testing

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Headlamp Switch Malfunction

  1. Ignition OFF, disconnect the harness connector at the headlamp and panel dimmer switch.
  2. Ignition OFF, verify that a test lamp illuminates between B+ and the ground circuit terminal 8.
    • If the test lamp does not illuminate, test the ground circuit for an open/high resistance.
  3. Ignition ON, verify the scan tool Headlamp Switch parameter is Inactive.
    • If not the specified value, test the signal circuit terminal 1 for a short to ground. If the circuit tests normal, replace the BCM.
  4. Verify the scan tool Auto Hdlp. Disable Sw. parameter is Inactive.
    • If not the specified value, test the signal circuit terminal 3 for a short to ground. If the circuit tests normal, replace the BCM.
  5. Install a 3 A fused jumper wire between the signal circuit terminal 1 and ground. Verify the scan tool Headlamp Switch parameter is Active.
    • If not the specified value, test the signal circuit for a short to voltage or an open/high resistance. If the circuit tests normal, replace the BCM.
  6. Install a 3 A fused jumper wire between the signal circuit terminal 3 and ground. Verify the scan tool Auto Hdlp. Disable Sw. parameter is Active.
    • If not the specified value, test the signal circuit for a short to voltage or and open/high resistance. If the circuit tests normal, replace the BCM.
  7. If all circuits test normal, test or replace the headlamp and panel dimmer switch.

Turn Signal/Multifunction Switch Malfunction

  1. Ignition OFF, disconnect the X2 harness connector at the turn signal/multifunction switch.
  2. Ignition OFF, verify that a test lamp illuminates between B+ and the ground circuit terminal D.
    • If greater than the specified range, test the ground circuit for an open/high resistance.
  3. Ignition ON, verify the scan tool Flash to Pass Switch parameter is Inactive.
    • If not the specified value, test the signal circuit terminal A for a short to ground. If the circuit tests normal, replace the BCM.
  4. Verify the scan tool High Beam Select Switch parameter is Inactive.
    • If not the specified value, test the signal circuit terminal E for a short to ground. If the circuit tests normal, replace the BCM.
  5. Install a 3 A fused jumper wire between the signal circuit terminal A and ground. Verify the scan tool Flash to Pass Switch parameter is Active.
    • If not the specified value, test the signal circuit for a short to voltage or an open/high resistance. If the circuit tests normal, replace the BCM.
  6. Install a 3 A fused jumper wire between the signal circuit terminal E and ground. Verify the scan tool High Beam Select Switch parameter is Active.
    • If not the specified value, test the signal circuit for a short to voltage or an open/high resistance. If the circuit tests normal, replace the BCM.
  7. If all circuits test normal, test or replace the turn signal/multifunction switch.

Headlamps Malfunction - Low Beam

  1. Ignition OFF, disconnect the HDLP LO/HID relay.
  2. Ignition ON, verify that a test lamp does not illuminate between the control circuit terminal 87 and ground.
    • If the test lamp illuminates, test the control circuit for a short to voltage.
  3. Verify that a test lamp illuminates between the B+ circuit terminal 85 and ground.
    • If the test lamp does not illuminate, test the B+ circuit for a short to ground or an open/high resistance.
  4. Verify that a test lamp illuminates between the B+ circuit terminal 30 and ground.
    • If the test lamp does not illuminate, test the B+ circuit for an open/high resistance.
  5. Connect a test lamp between the B+ circuit terminal 85 and the control circuit terminal 86.
  6. Command the Low Beams 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 ON, test the control circuit for a short to ground. If the circuit tests normal, replace the BCM.
    • If the test lamp is always OFF, test the control circuit for a short to voltage or an open/high resistance. If the circuit tests normal, replace the BCM.
  7. Ignition OFF, connect the HDLP LO/HID relay.
  8. Disconnect the harness connector at the appropriate headlamp.
  9. Ignition OFF, scan tool OFF, exterior lamps OFF, test for less than 5.0 Ω between each ground circuit terminal listed below and ground.
    • Ground circuit terminal F
    • Ground circuit terminal M
    • If greater than the specified range, test the ground circuit for an open/high resistance.
  10. Connect a test lamp between the control circuit terminal A and ground.
  11. Command the Low Beams 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 ON, test the control circuit for a short to voltage. If the circuit tests normal, replace the HDLP LO/HID relay.
    • 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 HDLP LO/HID relay.
  12. Ignition OFF, connect the harness connector at the headlamp.
  13. Command the Low Beams ON and OFF with a scan tool. The low beam headlamp should turn ON and OFF when changing between the commanded states.
    14. NOTE:

    Swap the control module from the other headlamp to test.

    • If any low beam LEDs do not illuminate, replace the headlamp control module.
    • If some of the low beam LEDs still do not illuminate, replace the headlamp assembly.

Headlamps Malfunction - High Beam

  1. Ignition OFF, disconnect the X4 connector at the underhood fuse block.
  2. Connect a test lamp between the control circuit terminal C3 and B+.
  3. Ignition ON, command the High Beams 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 ON, test the control circuit for a short to ground. If the circuit tests normal, replace the BCM.
    • If the test lamp is always OFF, test the control circuit for a short to voltage or an open/high resistance. If the circuit tests normal, replace the BCM.
  4. Ignition OFF, disconnect the harness connector at the appropriate headlamp.
  5. Ignition OFF, scan tool OFF, exterior lamps OFF, test for less than 5.0 Ω between each ground circuit terminal listed below and ground.
    • Ground circuit terminal F
    • Ground circuit terminal M
    • If greater than the specified range, test the ground circuit for an open/high resistance.
  6. Connect a test lamp between the control circuit terminal L and ground.
  7. Command the High Beams 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 ON, test the control circuit for a short to voltage. If the circuit tests normal, replace the underhood fuse block.
    • 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 underhood fuse block.
  8. Ignition OFF, connect the harness connector at the headlamp.
  9. Command the High Beams ON and OFF with a scan tool. The high beam headlamp should turn ON and OFF when changing between the commanded states.
    10. NOTE:

    Swap the control module from the other headlamp to test.

    • If any high beam LEDs do not illuminate, replace the headlamp control module.
    • If some of the high beam LEDs still do not illuminate, replace the headlamp assembly.

Headlamp Outage Detection Malfunction

  1. Ignition OFF, disconnect the harness connector at the appropriate headlamp assembly.
  2. Ignition ON, test for B+ between the signal circuit terminal C and ground.
    • If less than the specified value, test the signal circuit for a short to ground or an open/high resistance. If the circuit tests normal, replace the BCM.
  3. Ignition ON, verify that a test lamp does not illuminate between the signal circuit terminal C and ground.
    • If the test lamp illuminates, test the signal circuit for a short to voltage. If the circuit tests normal, replace the BCM.
  4. If all circuits test normal, test or replace the headlamp control module.
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