2002 Chevrolet Impala Owner's Manual - Page 177

Rear Window Defogger Press the button marked REAR to turn the defogger on. An indicator in the button will light. The rear window defogger and the outside rearview mirrors will automatically turn off after about 15 minutes. If you turn them on again, the defogger and the outside rearview mirrors will only stay on for about seven and one half minutes before turning off again. You can also turn them off by turning the ignition off or by pressing the button again. Do not attach anything like a temporary vehicle license or decal across the defogger grid. NOTICE: When turned on, the rear window defogger uses a warming grid to remove fog from the rear window. If your vehicle has the optional heated outside mirrors, they will heat to clear the surface of the mirrors. Don't use a razor blade or something else sharp on the inside of the rear window. If you do, you could cut or damage the warming grid, and the repairs wouldn't be covered by your warranty. Don't put decals there because you might have to scrape them off. 3-5