GMC 2002 Yukon XL Owner's Manual page 140

4. Press the COMP button on the bottom of the mirror
until the new zone number appears in the display.
After you stop pressing the button in, the display will
show a compass direction within a few seconds.
2-54
Outside Manual Adjust Mirrors
Adjust your outside mirrors so you can just see the side
of your vehicle and have a clear view of objects behind
you. The mirrors can be folded in to enter narrow areas.
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The use of hood mounted air deflectors and add
convex mirror attachments may adversely affect
mirror performance.
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on