One problem related to defogger has been reported for the 2005 GMC Envoy. The most recently reported issues are listed below.
Air conditioner quit working on level 5, would work on level 1-4, level 5 would keep turning off. Shortly after this within the same day I could smell something burning coming through the air vents. Mechanics noted and showed me that the resistor plugs on the back had burned and melted together, that's what was causing the burning smell. Needed a new resistor, pig tail, and blower. Also my fuel gauge and rpm are broke, have not been working for the past 3 years.