Circuit/System Testing

Rear Defogger Malfunction

1. Ignition OFF, disconnect the REAR DEFOG relay.
2. Ignition OFF, test for less than 1.0 ohm of resistance between the relay coil ground circuit and ground.
   • If greater than the specified range, test the relay coil ground circuit for an open/high resistance.
3. Connect a test lamp between the rear defogger relay control circuit and the relay coil ground circuit.
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 command states.
   • If the test lamp is always ON, test the rear defogger relay control circuit for a short to voltage. If the circuit tests normal, replace the BCM.
   • If the test lamp is always OFF, test the rear defogger relay 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, test or replace the REAR DEFOG relay.

Rear Defogger Indicator Malfunction

1. Ignition OFF, disconnect the harness connector C2 at the HVAC Control Assembly.
2. Ignition OFF, test for less than 1.0 ohm of resistance between the ground circuit terminal 9 and ground.
   • If greater than the specified range, test the ground circuit for an open/high resistance.
3. Disconnect the REAR DEFOG relay.
4. Connect a test lamp between the control circuit terminal 13 and ground.
5. 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.
6. If all circuits test normal, test or replace the HVAC Control Assembly.