Rear Window Defogger Operation
WARNING: This page is about a different car, the 2003 Oldsmobile Bravada, 2003 GMC Envoy XL, 2003 GMC Envoy, and 2003 Chevrolet TrailBlazer. However, it is still accessible from the selected car via links, so may be relevant.
Battery positive voltage is supplied through the LGM 2 fuse to the LGM for the rear window defogger system. When you turn the ignition to the ON position, and the rear window defogger switch is depressed. The HVAC control module illuminates the rear window defogger indicator and sends a class 2 message to the LGM to enable the rear window defogger system. The LGM enable the rear window defogger system by allowing battery positive voltage to the rear window defogger.
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 10 minute defogger cycles.