Heated Glass Element: Description and Operation

Rear Window Defogger Description and Operation

Rear Window Defogger System Components

The rear window defogger system consist of the following components:

* HVAC control module
* Body control module (BCM)
* RR DEFOG Relay
* Rear window defogger grid



Rear Window Defogger Operation

Battery negative voltage is supplied to the RR DEFOG relay control circuit from the BCM. With the engine running, the body control module (BCM) supplies negative voltage to RR DEFOG relay coil. When you depress the rear window defogger switch, the HVAC control module illuminates the rear window defogger indicator and sends a class 2 serial data message to the BCM. The BCM then energizes the RR DEFOG relay and allows battery positive voltage from the relay switched output to the RR DEFOG circuit to the rear window defogger grid. The output circuit is over current protected by the BATT MAIN 3 fuse in the fuse block underhood. Ground for the rear window defogger is provided by G301.


When you start the engine and press the rear window defogger switch for the first time, the defogger cycle lasts for 20 minutes. Further operation results in another 20 minute defogger cycle.


If battery voltage is low, the BCM will disable the rear window defogger by removing the battery negative voltage supplied to the RR DEFOG relay coil.