HVAC Control Module
WARNING: This page is about a different car, the 2003 GMC Sonoma, 2003 GMC Jimmy, 2003 Chevrolet S10 Pickup, and 2003 Chevrolet Blazer. However, it is still accessible from the selected car via links, so may be relevant.
Rear Defog Switch: The scan tool displays On or Off. When the rear defogger switch is pressed, the scan tool will display On. When the switch is released, the scan tool displays Off.