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Circuit/System Testing

  1. Ignition OFF, disconnect the RR Defog relay.
  2. Test for less than 1 Ω 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 a test lamp does not illuminate between the control circuit terminal 30 and ground.
    • If the test lamp illuminates, test the control circuit for a short to voltage.
  4. Verify 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 control circuit terminal 30 for a short to ground.
  5. Ignition OFF, disconnect the X2 harness connector at the rear window defogger grid.
  6. Test for less than 1 Ω 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. Ignition ON, connect a 40A fused jumper wire between the B+ circuit terminal 87 and the control 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 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 RR Defog relay.
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