2010 GMC Sierra 1500 Crew Cab Owner's Manual - Page 252

Sensors The interior temperature sensor, located in the headliner, measures the temperature of the air inside the vehicle. There is also an exterior temperature sensor located behind the front grille. This sensor reads the outside air temperature and helps maintain the temperature inside the vehicle. Any cover on the front of the vehicle could cause a false reading in the displayed temperature. The solar sensor, located in the defrost grille, in the middle of the instrument panel, monitors the solar heat. Do not cover the solar sensor or the system will not work properly. The climate control system uses the information from these sensors to maintain your comfort setting by adjusting the outlet temperature, fan speed, and the air delivery mode. The system may also supply cooler air to the side of the vehicle facing the sun. The recirculation mode will also be used as needed to maintain cool outlet temperatures. 4-28