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HOMESERVICE MANUALSCHEVROLET2008CHEVY EXPRESS G2500, VAN CARGO, 6.6 6REPAIR AND DIAGNOSISEXTERNAL PAGESDIFFERENT CARSECTION 2060 (LIGHTING SYSTEM)DIAGNOSTIC INFORMATION AND PROCEDURESTURN SIGNAL LAMPS AND/OR INDICATORS MALFUNCTIONCIRCUIT/SYSTEM TESTING
2008 Chevrolet Chevy Express G2500, Van Cargo, 6.6 6

Circuit/System Testing

2008 Chevrolet Chevy Express G2500, Van Cargo, 6.6 6SECTION 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.

Turn Signal Switch Malfunction

  1. Ignition OFF, disconnect the X1 harness connector at the turn signal/multifunction switch.
  2. Ignition OFF, verify that a test lamp illuminates between B+ and the ground circuit terminal F.
    • If the test lamp does not illuminate, test the ground circuit for an open/high resistance.
  3. Ignition ON, verify the scan tool Left Turn Signal 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 Right Turn Signal Switch parameter is Inactive.
    • If not the specified value, test the signal circuit terminal D 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 Left Turn Signal 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 D and ground. Verify the scan tool Right Turn Signal 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.

Turn Signal Lamps Malfunction

  1. Ignition OFF, disconnect the X4 harness connector at the BCM.
  2. Verify that a test lamp illuminates between the B+ circuit terminal 1 and ground.
    • If the test lamp does not illuminate, test the B+ circuit for a short to ground or an open/high resistance.
  3. Verify that a test lamp illuminates between the B+ circuit terminal 2 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 3 and ground.
    • If the test lamp does not illuminate, test the B+ circuit for a short to ground or an open/high resistance.
  5. Ignition OFF, connect the X4 harness connector at the BCM.
  6. Ignition OFF, disconnect the harness connector at the appropriate turn signal lamp.
  7. Ignition OFF, exterior lamps OFF, test for less than 5 Ξ© between the ground circuit terminal listed below and ground:
    • Park/Turn Signal Lamp - Terminal G
    • Tail/Stop and Turn Signal Lamp - Terminal GRD
    • If greater than the specified range, test the ground circuit for an open/high resistance.
  8. Connect a test lamp between the control circuit terminal listed below and ground:
    • Park/Turn Signal Lamp - Terminal MIN
    • Tail/Stop and Turn Signal Lamp - Terminal MJR
  9. Command the appropriate turn signal lamp 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 BCM.
    • 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 BCM.
  10. If all circuits test normal, replace the turn signal lamp.
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When to See a Mechanic

Stop DIY work and contact a certified mechanic immediately if any of the following apply:

  • β€’ You smell fuel, burning insulation, or see smoke.
  • β€’ Brakes feel soft, pull hard to one side, or make grinding noises.
  • β€’ The engine overheats, stalls repeatedly, or misfires under load.
  • β€’ You are missing required tools, torque specs, or safe lifting equipment.
  • β€’ You are not confident in the next step or safety outcome.