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Home >> GMC >> 2006 >> Sierra 1500 HD, RWD >> Repair and Diagnosis >> External Pages >> Different car >> Section 1548 (Lighting System) >> Diagnostic Information and Procedures >> Headlamps Malfunction >> Circuit/System Testing

Circuit/System Testing

WARNING: This page is about a different car, the 2010 GMC Sierra, 2010 GMC Cab & Chassis Sierra, 2010 Chevrolet Silverado, and 2010 Chevrolet Cab & Chassis Silverado. However, it is still accessible from the selected car via links, so may be relevant.

Headlamp Switch Malfunction

  1. Ignition OFF, disconnect the harness connector at the headlamp and panel dimmer switch.
  2. 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 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 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 an 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. Verify that a test lamp illuminates between B+ and the ground circuit terminal D.
    • If the test lamp does not illuminate, test the ground circuit for an open/high resistance.
  3. 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. 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.
  5. 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.
  6. 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.
  7. If all circuits test normal, test or replace the signal/multifunction switch.

Headlamps Malfunction - Low Beam

  1. Ignition OFF, disconnect the low beam 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 86 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. Disconnect the harness connector at the appropriate headlamp - low beam.
  6. Test for less than 5 Ω between the headlamp - low beam 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 - low beam.
  8. Connect a 20 A fused jumper wire between the B+ circuit terminal 30 and the control circuit terminal 87. Verify the headlamp - low beam is activated.
    • If the headlamp - low beam does not activate and the circuit fuse is good, test the control circuit for an open/high resistance. If the circuit tests normal, test or replace the headlamp - low beam.
    • If the headlamp - low beam does not activate and the circuit fuse is open, test the control circuit for a short to ground. If the circuit tests normal, test or replace the headlamp - low beam.
  9. Connect a test lamp between the B+ circuit terminal 86 and the control circuit terminal 85.
  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 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.
  11. If all circuits test normal, test or replace the low beam relay.

Headlamps Malfunction - High Beam

  1. Ignition OFF, disconnect the X4 harness connector at the fuse block-underhood.
  2. Connect a test lamp between the control circuit terminal C3 and B+.
  3. 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 open/high resistance. If the circuit tests normal, replace the BCM.
  4. Ignition OFF, connect the X4 harness connector at the fuse block-underhood. Disconnect the harness connector at the appropriate high beam headlamp.
  5. Ignition OFF, scan tool OFF, exterior lamps OFF, test for less than 5.0 Ω between the ground circuit terminal B and ground.
    • 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 A 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 fuse block-underhood.
    • If the test lamp is always OFF and the circuit fuse is good, test the control circuit for an open/high resistance. If the circuit tests normal, replace the fuse block-underhood.
    • If the test lamp is always OFF and the circuit fuse is open, test the control circuit for a short to ground. If the circuit tests normal, replace the high beam headlamp.
  8. If all circuits test normal, replace the high beam headlamp.
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