2009 Buick Lucerne Owner's Manual - Page 171

Rear Window Defogger The rear window defogger uses a warming grid to remove fog or frost from the rear window. Press to turn the rear window defogger on or off. An indicator light below the button comes on to show that the rear window defogger is on. Be sure to clear as much snow from the rear window as possible. The rear window defogger only works when the ignition is in ON/RUN. The rear window defogger stays on for about 20 minutes after the button is pressed if the vehicle is traveling at slower vehicle speeds. At higher vehicle speeds the rear window defogger may stay on continuously. If turned on again, the defogger only runs for about 10 minutes before turning off. The defogger can be turned off by pressing the button again, by turning the ignition to ACC/ACCESSORY or ON/RUN, or by turning off the engine. The heated outside rearview mirrors will heat to help clear fog or frost from the surface of the mirror when the rear window defogger is on. See Outside Heated Mirrors on page 2-37 for more information. Notice: Do not use a razor blade or sharp object to clear the inside rear window. Do not adhere anything to the defogger grid lines in the rear glass. These actions may damage the rear defogger. Repairs would not be covered by your warranty. < (Rear Defogger): 3-31