Rear Window Defogger Switch: Operation

WARNING: This page is about a different car, the 2004 Dodge Intrepid, 2004 Chrysler Intrepid, 2004 Chrysler Concorde, and 2004 Chrysler 300M. However, it is still accessible from the selected car via links, so may be relevant.

On Manual Temperature Control systems when the rear window defogger switch push button is depressed, it provides a hard wired signal by momentarily closing the rear window defogger switch sense circuit which is monitored by the BCM. On Automatic Temperature Control (ATC) systems, when the defogger switch is depressed, the ATC head sends a switch status message to the BCM over the Programmable Communications Interface (PCI) data bus network. A Light Emitting Diode (LED) in the push button for the rear window defogger switch illuminates to indicate when the rear window defogger system is turned on. Each time the BCM rear window defogger timer and logic circuitry sees another request, it toggles a control output to the rear window defogger relay. Energizing the rear window defogger relay provides electrical current to the rear window defogger grid and to the LED indicator in the switch, which lights to indicate when the defogger system is turned on. A dedicated fuse in the junction block protects the rear window defogger relay output circuit to the LED indicator.