Cadillac 2004 CTS Owner's Manual page 151

Sensors
There is a solar sensor located on the instrument panel,
near the windshield.
These sensors monitor the solar radiation and the
air inside your vehicle, then use the information to
maintain the selected temperature by initiating needed
adjustments to the temperature, the fan speed and
the air delivery system. The system may also supply
cooler air to the side of the vehicle facing the sun.
The recirculation mode will also be activated, as
necessary. Do not cover the sensors or the automatic
climate control system will not work properly.
There is also an interior
temperature sensor
located to the right of the
steering wheel on the
instrument panel.
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