Your vehicle may have an automatic dimming rearview mirror with a compass. This feature enables the mirror to sense nighttime glare from vehicle headlamps from behind and automatically dim to reduce the glare to a safe level. The automatic dimming feature turns on each time the vehicle is started.

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 indicator light, located to the left of the on/off button, is on. If it's not, press and hold the on/off button until the 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 until the indicator light turns off.

Press the on/off button once to turn the compass on or off.

When the ignition and the compass feature are on, the compass will show two character boxes for a few seconds. After a few seconds, the mirror will display the current compass direction.

If after a few seconds the display does not show a compass direction, (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, note pad holder, or similar object. If the letter C or CAL appears in the compass window, the compass may need to be reset or calibrated.

The compass can be calibrated by driving the vehicle in circles at 5 mph (8 km/h) or less until the display reads a direction.

Compass variance is the difference between earth's magnetic north and true geographic north. If the mirror is not adjusted for compass variance, the compass could give false readings.

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 the vehicle is driven outside zone eight. Under certain circumstances, such as a long distance, cross-country trip, it will be necessary to adjust the compass variance.

To adjust for compass variance, do the following:

1. Find your current location and variance zone number on the zone map. See Automatic Dimming Rearview Mirror with OnStar® and Compass for map information.
2. Press and hold the on/off button until a zone number appears on the display.
3. Once the zone number appears on the display, press the on/off button quickly until you reach the correct zone number. If C or CAL appears in the compass window, the compass may need calibration. See "Compass Calibration" listed previously.