The rear window defogger system consists of the following components:

Battery positive voltage is supplied at all times from the rear defog 3 fuse in the rear fuse block to the switch side of the REAR DEFOG relay in the rear fuse block. When the rear defogger switch is pressed in the HVAC control module. The HVAC then applies a ground to the REAR DEFOG relay. This energizes the relay and allows the battery positive voltage to be applied through the switched side of the relay to the rear window defogger grid. The rear window defogger grid is grounded at all times at G307 and G306.

The rear window defogger will turn off automatically after it has been activated. This time is determined by a dynamic timer which varies the amount of time the rear window defogger is allowed to be on based on ambient temperature and vehicle speed. The rear window defogger will be extended when the ambient temperature is cooler or while the vehicle is in motion.

If the battery is low, the BCM will send a signal to the HVAC, which in turn will disable the rear window defogger by not providing voltage to the REAR DEFOG relay.