Rear Window Defogger Switch: Operation
WARNING: This page is about a different car, the 2004 Dodge Grand Caravan, 2004 Dodge Caravan, and 2004 Chrysler Town & Country. However, it is still accessible from the selected car via links, so may be relevant.
An LED indicator will illuminate when the rear window defogger switch is activated. The switch energizes the A/C-heater control module which then requests the front control module (FCM) to activate the rear window defogger relay via the J1850 communication bus. The rear window defogger relay controls the current to flow to the grids of the rear window defogger and the heated power side view mirrors. The defogger relay will be on for approximately 10 minutes or until the control switch or ignition is turned off.