2012 GMC Sierra Owner's Manual - Page 276

8-10 Climate Controls 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 climate control system uses the information from these sensors to maintain comfort settings 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. Air Vents Use the air outlets located in the center and on the side of the instrument panel to direct the airflow. Use the thumbwheels near the air outlets to open or close off the airflow. Operation Tips . The interior temperature sensor, located in the headliner, measures the temperature of the air inside the vehicle. Clear away any ice, snow, or leaves from air inlets at the base of the windshield that could block the flow of air into the vehicle. Keep the path under the front seats clear of objects to help circulate the air inside of the vehicle more effectively. Use of non‐GM approved hood deflectors can adversely affect the performance of the system. Check with your dealer before adding equipment to the outside of the vehicle. . .