GMC 2008 Savana Van Owner's Manual page 162

To adjust for compass variance, use the following
procedure:
Compass Variance (Zone) Procedure
1. Do not set the compass zone when the vehicle is
moving. Only set it when the vehicle is in PARK (P).
Press the vehicle information button until PRESS
V
TO CHANGE COMPASS ZONE displays.
2. Find the vehicle's current location and variance
zone number on the map.
Zones 1 through 15 are available.
3-48
3. Press the set/reset button to scroll through and
select the appropriate variance zone.
4. Press the trip/fuel button until the vehicle heading,
for example, N for North, is displayed in the DIC.
5. If calibration is necessary, calibrate the compass.
See "Compass Calibration Procedure" following.
Compass Calibration
The compass can be manually calibrated. Only calibrate
the compass in a magnetically clean and safe location,
such as an open parking lot, where driving the vehicle
in circles is not a danger. It is suggested to calibrate
away from tall buildings, utility wires, manhole covers,
or other industrial structures, if possible.
If CAL should ever appear in the DIC display, the
compass should be calibrated.
If the DIC display does not show a heading, for example,
N for North, or the heading does not change after
making turns, there may be a strong magnetic field
interfering with the compass. Such interference may
be caused by a magnetic CB or cell phone antenna
mount, a magnetic emergency light, magnetic note
pad holder, or any other magnetic item. Turn off
the vehicle, move the magnetic item, then turn on
the vehicle and calibrate the compass.