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HOMESERVICE MANUALSCHEVROLET2008CHEVY EXPRESS G3500, VAN PASSENGER EXTENDEDREPAIR AND DIAGNOSISEXTERNAL PAGESDIFFERENT CARSECTION 602 (FIXED AND MOVEABLE WINDOWS SYSTEM)DIAGNOSTIC INFORMATION AND PROCEDURESREAR WINDOW DEFOGGER MALFUNCTIONCIRCUIT/SYSTEM TESTING
2008 Chevrolet Chevy Express G3500, Van Passenger Extended

Circuit/System Testing

2008 Chevrolet Chevy Express G3500, Van Passenger ExtendedSECTION Circuit/System Testing
WARNING: This page is about a different car, the 2010 Cadillac STS. However, it is still accessible from the selected car via links, so may be relevant.
  1. Ignition OFF, disconnect the REAR DEFOG relay.
  2. Ignition ON, verify that a test lamp does not illuminate between the control circuit terminal R8 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 R7 and ground.
    • If the test lamp does not illuminate, test the relay switch B+ circuit for a short to ground or an open/high resistance. If the circuit tests normal and the B+ circuit fuse is open, test the control circuit terminal R8 for a short to ground.
  4. Verify that a test lamp illuminates between the ignition circuit terminal R6 and ground.
    • If the test lamp does not illuminate, test the ignition circuit for a short to ground or an open/high resistance.
  5. Ignition OFF, disconnect the X1 harness connector at the rear window defogger grid.
  6. Test for less than 5 ohms between the ground circuit terminal B and ground.
    • If greater than the specified range, test the ground circuit for an open/high resistance.
  7. Connect the X1 harness connector at the rear window defogger grid.
  8. Disconnect the X2 harness connector at the rear window defogger grid.
  9. Test for less than 5 ohms between the ground circuit terminal A and ground.
    • If greater than the specified range, test the ground circuit for an open/high resistance.
  10. Connect the X2 harness connector at the rear window defogger grid.
  11. Ignition ON, connect a 40 A fused jumper wire between the B+ circuit terminal R7 and the control circuit terminal R8. Verify the rear window defogger grid is activated.
    • If the rear window defogger grid does not activate, test the control circuit for an open/high resistance. If the circuit tests normal, test or replace the rear window defogger grid.
  12. Connect a test lamp between the ignition circuit terminal R7 and the control circuit terminal R10.
  13. Command the Rear Defog Relay 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 RIM.
    • 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 RIM.
  14. If all circuits test normal, test or replace the REAR DEFOG relay.
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