2009 GMC Yukon Owner's Manual - Page 201

Automatic Headlamp System When it is dark enough outside, the automatic headlamp system turns on the headlamps at the normal brightness, along with the taillamps, sidemarker, parking lamps, and the instrument panel lights. The radio lights will also be dim. To turn off the automatic headlamp system, turn the exterior lamps switch to the off position and then release it. For vehicles first sold in Canada, the transmission must be in the P (Park) position, before the automatic headlamp system can be turned off. 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, heavy overcast weather, or a tunnel. 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 will come 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 3-19. 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). See DIC Vehicle Customization (With DIC Buttons) on page 3-74. The regular headlamp system can be turned on when needed. 3-17