2010 GMC Sierra 1500 Crew Cab Owner's Manual - Page 237

The vehicle has a light sensor located on the top of the instrument panel in the defroster grille that regulates when the automatic headlamps turn on. Do not cover the sensor or the headlamps will come on whenever the ignition is on. The system may also turn on the headlamps when driving through a parking garage or heavy overcast weather. This is normal. There is a delay in the transition between the daytime and nighttime operation of the Daytime Running Lamps (DRL) and the automatic headlamp systems so that driving under bridges or bright overhead street lights does not affect the system. The DRL and automatic headlamp system is only affected when the light sensor detects a change in lighting lasting longer than the delay. If the vehicle is started in a dark garage, the automatic headlamp system comes on immediately. Once the vehicle leaves the garage, it takes approximately one minute for the automatic headlamp system to change to DRL if it is bright enough outside. During that delay, the instrument panel cluster may not be as bright as usual. Make sure the instrument panel brightness control is in the full bright position. See Instrument Panel Brightness on page 4‑15. To idle the vehicle with the automatic headlamp system off, turn the control to the off position. The headlamps will also stay on after you exit the vehicle. This feature can be programmed using the Driver Information Center (DIC), if equipped. See DIC Vehicle Customization (With DIC Buttons) on page 4‑76. If the vehicle is not equipped with DIC buttons, exit lighting is automatic. When it is dark enough outside, the exterior lamps remain on for 30 seconds after the ignition is moved from ON/RUN to LOCK/OFF. For vehicles without a radio, the instrument panel light remains on for 30 seconds with the driver's door closed. For vehicles with a radio, the instrument panel light remains on for 10 minutes with the driver's door closed. See Retained Accessory Power (RAP) on page 3‑25. The regular headlamp system can be turned on when needed. 4-13