2010 GMC Sierra 1500 Crew Cab Owner's Manual - Page 236

Headlamps on Reminder For vehicles with a radio, a reminder chime sounds when the headlamps or parking lamps are manually turned on, the ignition is off and a door is open. To disable the chime, turn the light off. When the DRL system is on, only the DRL lamps are on. The taillamps, sidemarker, instrument panel lights, and other lamps will not be on. When it begins to get dark, the automatic headlamp system switches 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 P (Park) position, before the DRL lamps can be turned off. Daytime Running Lamps (DRL) Daytime Running Lamps (DRL) can make it easier for others to see the front of your vehicle during the day. Fully functional daytime running lamps are required on all vehicles first sold in Canada. The DRL system comes on when the following conditions are met: ... 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 ignition is on. The exterior lamps control is in AUTO. The engine is running. The light sensor determines it is daytime. 4-12