Circuit/System Testing

Rear Defogger Malfunction

1. Ignition OFF, disconnect the RR DEFOG relay.
2. Ignition OFF, test for less than 1.0 ohm of resistance between the coil side ground circuit terminal and ground.
   • If greater than the specified range, test for an open/high resistance.
3. Ignition ON, verify that a test lamp does not illuminate between the switch side control circuit terminal 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 switch side B+ circuit terminal and ground.
   • If the test lamp does not illuminate, test the switch side B+ circuit for a short to ground or an open/high resistance. If the circuit tests normal and the switch side circuit fuse is open, test the switch side control circuit terminal for a short to ground.
5. Connect a test lamp between the coil side control circuit terminal and the coil side ground circuit terminal.
6. Command the RR 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.
7. If all circuits test normal, test or replace the RR DEFOG relay.