GMC Sierra Denali Owner's Manual page 111

Compass Calibration
The compass may need calibration if one of the
following occurs:
After approximately five seconds, the display does
not show a compass heading (N for North, for
example), there may be a strong magnetic field
interfering with the compass. Such interference may
be caused by a magnetic antenna mount, magnetic
note pad holder or a similar magnetic item.
The compass does not display the correct heading
and the compass zone variance is set correctly.
In order to calibrate, CAL must be displayed in the
mirror compass windows. If CAL is not displayed, push
the
on/off
button for approximately 12 seconds or
until CAL is displayed.
The compass can be calibrated in one of two ways:
Drive the vehicle in circles at 5 mph (8 km/h)
or
less
until the display reads a direction, or
@
drive the vehicle on your everyday routine and after
several turns the compass will become calibrated
and will display a direction.
Passenger Air Bag Indicator
Your vehicle may be equipped with a passenger air bag
indicator, on the mirror glass, just above the buttons.
If your vehicle has this feature, the mirror will display the
word ON, or an air bag symbol in Canada, when the
passenger air bag is engaged. For more information,
see Passenger Sensing System on page 1-68.
Cleaning the Mirror
When cleaning the mirror, use a paper towel or similar
material dampened with glass cleaner. Do not spray
glass cleaner directly on the mirror as that may cause
the liquid cleaner to enter the mirror housing.
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