GMC 2007 Sierra 1500 Pickup Owner's Manual page 177

To adjust between Fahrenheit and Celsius do the
following:
1. Press and hold the on/off button for
approximately four seconds until either a
flashing F or C appears.
2. Press the button again to change the display
to the desired unit of measurement. After
approximately four seconds of inactivity, the
new unit will be locked in and the
compass/temperature display will return.
If an abnormal temperature reading is displayed
for an extended period of time, please consult your
dealer. Under certain circumstances, a delay in
updating the temperature is normal.
Automatic Dimming Mirror Operation
The automatic dimming mirror function is turned on
automatically each time the ignition is started.
To operate the automatic dimming 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 approximately
six seconds until the green light comes on,
indicating that the mirror is in automatic
dimming mode.
2. Turn off the automatic dimming mirror function
by pressing and holding the on/off button for
approximately six seconds, until the green
indicator light turns off.
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