Circuit/System Testing

Rear Window Defogger Switch Malfunction

1. Ignition ON, with a scan tool observe the rear defog status parameter while turning the rear defogger switch ON and OFF. The reading should change between ON and OFF.
   • If the reading does not change as the switch is activated, replace the HVAC control module.
2. Ignition ON, observe the rear defogger switch indicator while turning the rear defogger switch ON and OFF. The indicator should turn ON and OFF as the switch is activated.
   • If the rear defogger switch indicator does not illuminate, replace the HVAC control module.

Rear Window Defogger Malfunction

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 relay switch 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 relay switch B+ circuit fuse is open, test the relay controlled output circuit terminal R8 for a short to ground.
4. Ignition ON, verify that a test lamp illuminates between the relay coil B+ circuit terminal R6 and ground.
   • If the test lamp does not illuminate, test the relay coil B+ 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. Ignition OFF, all doors closed, test for less than 5.0 ohms of resistance between the rear window defogger grid 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. Ignition OFF, disconnect the X2 harness connector at the rear window defogger grid.
9. Ignition OFF, all doors closed, test for less than 5.0 ohms 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.
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. Ignition OFF, connect a test lamp between the relay B+ circuit terminal R7 and the relay control circuit terminal R10.
13. 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 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.