Rear Window Defogger

Rear Window Defogger Description and Operation

Rear Window Defogger

The rear window defogger system consists of the following components:

* Body Control Module (BCM)
* Electronic compass
* HVAC control module
* Instrument Panel Cluster (IPC)
* Rear window defogger grid
* REAR WINDOW DEFOGGER relay

Battery positive voltage is supplied at all times from the BATT MAIN 3 fuse in the underhood fuse block to the coil and switch side of the REAR WINDOW DEFOGGER relay in the instrument panel (I/P) fuse block. When the rear defogger switch is pressed in the HVAC control module, a class 2 data signal is sent to the BCM. The BCM then applies a ground to the REAR WINDOW DEFOGGER 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 G301.

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 disable the rear window defogger by removing the ground supplied to the REAR WINDOW DEFOGGER relay.