Rear Window Defogger Operation

WARNING: This page is about a different car, the 2002 GMC Sierra, 2002 GMC Cab & Chassis Sierra, 2002 Chevrolet Silverado, and 2002 Chevrolet Cab & Chassis Silverado. However, it is still accessible from the selected car via links, so may be relevant.

When you turn the ignition to the ON position, ignition 1 voltage is supplied through the IGN E fuse to the RR DEFOG relay coil. Battery positive voltage is supplied at all times to the RR DEFOG relay switch. When the rear window defogger switch is depressed, the HVAC control module illuminates the rear window defogger indicator and energizes the RR DEFOG relay by grounding the control circuit of the relay. This allows battery positive voltage through the RR DEFOG fuse to the rear window defoggers. Ground for the rear window defogger is provided by G306 or G390.

When you turn ON the ignition and press the rear window defogger switch for the first time, the defogger cycle lasts 10 minutes. Further operation results in 5 minute defogger cycles.