Circuit/System Testing

Ignition OFF, disconnect the X2 harness connector at the HVAC control module.
Disconnect the RR DEFOG relay.
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.
Connect a test lamp between the control circuit terminal 86 and ground circuit terminal 85.
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.
Ignition OFF, connect the X2 harness connector at the HVAC control module.
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 or always OFF, replace the HVAC control module.
If all circuits test normal, test or replace the RR DEFOG relay.