Cadillac CTS Navigation Manual page 65

The navigation system determines
the position of the vehicle by using
satellite signals, various vehicle
signals, and map data.
At times, other interferences such
as the satellite condition, road
configuration, the condition of the
vehicle and/or other circumstances
can interfere with the navigation
system's ability to determine the
accurate position of the vehicle.
The GPS shows the current position
of the vehicle using signals sent by
the GPS Satellites of the United
States Department of Defense.
When the vehicle is not receiving
signals from the satellites, a symbol
appears on the map screen. Refer
to Symbols.
This system may not be available or
interferences may occur if any of the
following is true:
Signals are obstructed by tall
buildings, trees, large trucks,
or a tunnel.
Objects are located on the rear
shelf of the vehicle.
Satellites are being repaired or
improved.
After-market glass tinting has
been applied to the vehicle's
rear windshield.
For more information if the GPS is
not functioning properly, see If the
System Needs Service and
Problems with Route Guidance.
At times, the position of the vehicle
on the map may be inaccurate due
to one or more of the following
reasons:
The road system has changed.
The vehicle is driving on slippery
road surfaces such as in sand,
gravel and/or snow.
The vehicle is traveling on
winding roads.
The vehicle is on a long
straight road.
The vehicle is approaching a tall
building or a large vehicle.
The surface streets run parallel
to a freeway.