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Home >> Chevrolet >> 2020 >> Express 2500 LS, 6.0L Eng VIN G >> Repair and Diagnosis >> External Pages >> Different car >> Section 18 (Lighting System) >> Diagnostic Information and Procedures >> Headlamps Malfunction >> Circuit/System Testing

Circuit/System Testing

WARNING: This page is about a different car, the 2019 GMC Savana 3500, 2019 GMC Savana 2500, 2019 Chevrolet Express 3500, and 2019 Chevrolet Express 2500. 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. Test for less than 5 Ω 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 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.
  4. Ignition ON, verify the scan tool Headlamp ON 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.
  5. Ignition ON, verify the scan tool Parklamp Switch parameter is Inactive.
    • If not the specified value, test the signal circuit terminal 2 for a short to ground. 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 Parklamp 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. Install a 3 A fused jumper wire between the signal circuit terminal 2 and ground. Verify the scan tool Parklamp 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.
  8. Install a 3 A fused jumper wires 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 terminal 1 for a short to voltage or an open/high resistance. If the circuit tests normal, replace the BCM.
  9. If all circuits test normal, 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. Test for less than 5 Ω 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 Flash to Pass 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. Ignition ON, verify the scan tool High Beam Select Switch parameter is Inactive.
    • If not the specified value, test the signal circuit terminal C 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 Flash to Pass Switch 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.
  6. Install a 3 A fused jumper wire between the signal circuit terminal C 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 and 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.

Headlamp Malfunction - Low Beam

  1. Ignition OFF, disconnect the X3 harness connector at the underhood fuse block.
  2. Connect a test lamp between the relay control circuit terminal H4 and B+.
  3. Ignition ON, command the Low Beams ON and OFF with a scan tool. The test lamp should turn ON and OFF 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, connect the X3 harness connector at the underhood fuse block.
  5. Ignition OFF, disconnect the harness connector at the appropriate low beam headlamp.
  6. Test for less than 5 Ω between the ground circuit terminal listed below and ground.
    • Terminal B - with V22
    • Terminal A - w/o V22
    • If greater than the specified range, test the ground circuit for an open/high resistance.
  7. Connect a test lamp between the appropriate control circuit terminal listed below and ground.
    • Terminal A - with V22
    • Terminal C - w/o V22
  8. Ignition ON, command the Low Beams ON and OFF with a scan tool. The test lamp should turn ON and OFF 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.
  9. If all circuits test normal, test or replace the low beam headlamp.

Headlamp Malfunction - High Beam

  1. Ignition OFF, disconnect the X3 harness connector at the underhood fuse block.
  2. Connect a test lamp between the relay control circuit terminal K8 and B+.
  3. Ignition ON, command the High Beams ON and OFF with a scan tool. The test lamp should turn ON and OFF 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, connect the X3 harness connector at the underhood fuse block.
  5. Ignition OFF, disconnect the harness connector at the appropriate high beam headlamp.
  6. Test for less than 5 Ω between the ground circuit terminal listed below and ground.
    • Terminal B - with V22
    • Terminal A - w/o V22
    • If greater than the specified range, test the ground circuit for an open/high resistance.
  7. Connect a test lamp between the control circuit terminal listed below and ground.
    • Terminal A - with V22
    • Terminal B - w/o V22
  8. Ignition ON, command the High Beams ON and OFF with a scan tool. The test lamp should turn ON and OFF 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.
  9. If all circuits test normal, test or replace the high beam headlamp.
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