2008 GMC Sierra 1500 Pickup Owner's Manual - Page 152

Daytime Running Lamps (DRL) Daytime Running Lamps (DRL) can make it easier for others to see the front of your vehicle during the day. DRL can be helpful in many different driving conditions, but they can be especially helpful in the short periods after dawn and before sunset. Fully functional daytime running lamps are required on all vehicles first sold in Canada. The DRL system will come on when the following conditions are met: Automatic Headlamp System When it is dark enough outside, the automatic headlamp system will turn 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 PARK (P) 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. Be sure it is not covered, 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 will only be affected when the light sensor detects a change in lighting lasting longer than the delay. The ignition is on. The exterior lamps control is in AUTO. The transmission is not in PARK (P). The light sensor determines it is daytime. When the DRL are on, only the DRL lamps will be on. The taillamps, sidemarker, and other lamps will not be on. The instrument panel will not be lit up either. When it begins to get dark, the automatic headlamp system will switch from DRL to the headlamps. To turn off the DRL lamps, turn the exterior lamps control to the OFF position and then release. For vehicles first sold in Canada, the transmission must be in the PARK (P) position, before the DRL lamps can be turned off. 3-16