1998 Buick LeSabre Owner's Manual - Page 146

Rear Window Defogger The lines you see on the rear window warm the glass. Pressthis button to start warming your window. Do not attach a temporary vehicle license, tape or decals across the defogger grid on the rear window. NOTICE: Do not try to clear frost or other material from the inside of the rear window with a razor blade or anything else that is sharp. This damage may the rear defogger grid. The repairs wouldn't be covered by your warranty. After 10 minutes it will turn off by itself, or pressing the button during the heating cyclewill turn it off. If you need additional warming time, push the button again. The systemwill then operate for five minutes before going off by itself. 3-10