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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 >> Headlamps Malfunction >> 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.

Headlamp Switch Circuit Test

  1. Ignition OFF, disconnect the harness connector at the headlamp switch.
  2. Test for less than 1 ohm of resistance between the ground circuit terminal 8 and ground.
    • If greater than the specified range, 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. Install a 3A fused jumper wire between the signal circuit terminal 1 and the ground circuit terminal 8. 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.
  5. If all circuits test normal, test or replace the headlamp switch.

High/Low Beam Select Switch Circuit Test

  1. Ignition OFF, disconnect the harness connector X2 at the turn signal/multifunction switch.
  2. Test for less than 1 ohm of resistance between the ground circuit terminal D and ground.
    • If greater than the specified range, test the ground circuit for an open/high resistance.
  3. Ignition ON, 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.
  4. Install a 3A fused jumper wire between the signal circuit terminal E and the ground circuit terminal D. 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.
  5. If all circuits test normal, test or replace the signal/multifunction switch.

Low Beam Headlamp Circuit Test

  1. Ignition OFF, disconnect the headlamp low/HID relay.
  2. Ignition ON, verify that a test lamp does not illuminate between the headlamp control circuit terminal 87 and ground.
    • If the test lamp illuminates, test the headlamp control circuit for a short to voltage.
  3. Verify that a test lamp illuminates between the B+ circuit terminal 30 and ground.
    • If the test lamp does not illuminate, replace the underhood fuse block.
  4. Verify that a test lamp illuminates between the B+ circuit terminal 85 and ground.
    • If the test lamp does not illuminate, replace the underhood fuse block.
  5. Disconnect the harness connector at the affected headlamp.
  6. Test for less than 1 ohm of resistance between the headlamp ground circuit terminal B and ground.
    • If greater than the specified range, test the ground circuit for an open/high resistance.
  7. Connect the harness connector at the headlamp.
  8. Connect a 20A fused jumper wire between the B+ circuit terminal 30 and the headlamp control circuit terminal 87. Verify the low beam headlamps are on.
    • If the headlamps do not turn on, test the control circuit for an open/high resistance. If the circuit tests normal, test or replace the affected headlamp.
  9. Connect a test lamp between the B+ circuit terminal 85 and the relay control circuit terminal 86.
  10. 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 relay control circuit for a short to ground. If the circuit tests normal, replace the BCM.
    • If the test lamp is always OFF, test the relay control circuit for a short to voltage or an open/high resistance. If the circuit tests normal, replace the BCM.
  11. If all circuits test normal, test or replace the headlamp low/HID relay.

High Beam Relay Control Circuit Test

  1. Ignition OFF, disconnect the harness connector X4 at the BCM.
  2. Low beam headlamps ON, verify the high beam headlamps are not on.
    • If the high beam headlamps are on, test the high beam relay control circuit for a short to ground. If the circuit tests normal replace the underhood fuse block.
  3. Install a 10A fused jumper wire between the relay control circuit terminal 16 and ground. Verify the high beam headlamps are on.
    • If the high beam headlamps are not on, test the high beam relay control circuit for an open/high resistance. If the circuit tests normal replace the underhood fuse block.
  4. If all circuits test normal, replace the BCM.

High Beam Headlamp Circuit Test

  1. Ignition OFF, disconnect the harness connector at the affected headlamp.
  2. Test for less than 1 ohm of resistance between the ground circuit terminal B and ground.
    • If greater than the specified range, test the ground circuit for an open/high resistance.
  3. Connect a test lamp between the control circuit terminal A and the ground circuit terminal B.
  4. 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.
  5. If all circuits test normal, test or replace the affected headlamp.
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