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Circuit/System Testing

Rear Window Defogger Switch Malfunction

  1. Ignition OFF, disconnect the C2 harness connector at the HVAC control module.
  2. Ignition ON, verify the scan tool rear defog switch parameter is OFF.
    • If not the specified value, test the signal circuit terminal J for a short to ground. If the circuit tests normal, replace the BCM.
  3. Install a 3A fused jumper wire between the signal circuit terminal J and ground. Verify the scan tool rear defog switch parameter is ON.
    • If not the specified value, test the signal circuit terminal J for a short to voltage or an open/high resistance. If the circuit tests normal, replace the BCM.
  4. If all circuits test normal, replace the HVAC control module.

Rear Window Defogger Malfunction

  1. Ignition OFF, disconnect the rear window defog relay.
  2. Test for less than 1.0 ohm of resistance between the rear defog relay coil side ground circuit and ground.
    • If greater than the specified range, test the ground circuit for an open/high resistance.
  3. Ignition ON, verify that a test lamp does not illuminate between the relay switch controlled output circuit and ground.
    • If the test lamp illuminates, test the control circuit for a short to voltage.
  4. Verify that a test lamp illuminates between the relay switch B+ circuit terminal 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 relay switch B+ circuit fuse is open, test the relay switch controlled output circuit for a short to ground. If the circuit tests normal, test or replace the rear defog relay.
  5. Ignition OFF, disconnect the C2 harness connector at the rear window defogger grid.
  6. Test for less than 1.0 ohm of resistance between the rear window defogger grid ground circuit terminal A and ground.
    • If greater than the specified range, test the ground circuit for an open/high resistance.
  7. Connect the C2 harness connector at the rear window defogger grid.
  8. Connect a 20A fused jumper wire between the relay switch B+ circuit and the relay switch controlled output circuit. 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.
  9. Connect a test lamp between the rear defog relay control circuit and ground.
  10. Command the rear window 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 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.
  11. If all circuits test normal, test or replace the rear defog relay.

Rear Window Defogger Indicator Malfunction

  1. Ignition OFF, disconnect the C2 harness connector at the HVAC control module.
  2. Disconnect the rear defog relay.
  3. Connect a test lamp between the control circuit terminal F and ground.
  4. Ignition ON, command the rear window defogger 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.
  5. If all circuits test normal, replace the HVAC control module.
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