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Circuit/System Testing

WARNING: This page is about a different car, the 2011 Cadillac DTS. However, it is still accessible from the selected car via links, so may be relevant.
  1. Ignition OFF, disconnect the REAR DEFOG relay.
  2. Test for less than 1 ohm between the ground circuit terminal 85 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 control circuit terminal 87 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 30 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 control circuit terminal 87 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.
  6. Test for less than 1 ohm 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 harness connector at the rear window defogger.
  8. Ignition ON, connect a 40A fused jumper wire between the B+ circuit terminal 30 and the control circuit terminal 87. 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 control circuit terminal 86 and the ground circuit terminal 85.
  10. Command the Rear Defog Request 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 HVAC control module.
    • 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 HVAC control module.
  11. If all circuits test normal, test or replace the REAR DEFOG relay.
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