GMC 2002 Sierra - Manual (Page 159)

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Electrochromic Mirror Operation
The electrochromic (self dimming) mirror function is
turned on automatically each time the ignition is started.
To operate the electrochromic mirror do the following:
1. Make sure the green indicator light, located to the
left of the on/off button, is lit. If it’s not, press and
hold the on/off button for six seconds until the green
light comes on, indicating that the mirror is in
electrochromic (self dimming) mode.
2. Turn off the electrochromic mirror function by
pressing and holding the on/off button for
six seconds until the green indicator light turns off.
Compass Variance
The mirror is set in zone eight upon leaving the factory.
It will be necessary to adjust the compass to compensate
for compass variance if you live outside of zone eight.
Under certain circumstances, as during a long distance
cross
- country trip, it will be necessary to adjust for
compass variance. Compass variance is the difference
between earth’s magnetic north and true geographic
north. If not adjusted to account for compass variance,
your compass could give false readings.
To adjust for compass variance do the following:
1. Find your current location and variance zone number
on the following zone map.
2. Press and hold the on/off button for nine seconds or
until a Z and a zone number appears in the display.
The compass is now in zone mode.
3. Keep pressing the on/off button until the desired
zone number appears in the display. Release the
button. After about four seconds of inactivity, the
new zone number will be locked in and the
comp/temp display will return.
4. Calibrate the compass as described below.