Diagnostic Aids

WARNING: This page does not describe the selected car, but rather 8 other vehicles, including the 2011 GMC Yukon XL, 2011 GMC Yukon, 2011 Chevrolet Tahoe, 2011 Chevrolet Suburban, and 2011 Chevrolet Avalanche. However, it is still accessible from the selected car via links, so may be relevant.

Check for aftermarket equipment installed or personal items that could create a magnetic field that could affect the performance of the compass.
Cycle the ignition before performing the compass magnetic variation adjustment procedure.
Check that the compass module is properly installed in the vehicle. The embossed arrow on the module should be parallel with the centerline of the vehicle.