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Circuit/System Testing

Rear Window Defogger Switch Malfunction

  1. Ignition OFF, disconnect the X2 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. Ignition OFF, test for less than 5.0 ohms of resistance between the ground circuit terminal 86 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 controlled output circuit terminal 30 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 B+ circuit terminal 87 and ground.
    • If the test lamp does not illuminate, test the 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 controlled output circuit terminal 30 for a short to ground. If the circuit tests normal, test or replace the rear defog relay.
  5. Ignition OFF, disconnect the X2 harness connector at the rear window defogger grid.
  6. Ignition OFF, test for less than 5.0 ohms of resistance between the ground circuit terminal A and ground.
    • If greater than the specified range, test the ground circuit for an open/high resistance.
  7. Connect the X2 harness connector at the rear window defogger grid.
  8. Connect a 20A fused jumper wire between the B+ circuit terminal 87 and the controlled output circuit terminal 30. 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 relay control circuit terminal 85 and ground.
  10. 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 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 X2 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 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.
  5. If all circuits test normal, replace the HVAC control module.
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