2010 GMC Sierra 1500 Crew Cab Owner's Manual - Page 521

It is recommended that the vehicle is taken to your dealer for service if the headlamps need to be adjusted. It is possible however, to re-aim the headlamps as described. The vehicle should: . Headlamp aiming is done with the vehicle's low-beam headlamps. The high-beam headlamps will be correctly aimed if the low-beam headlamps are aimed properly. To adjust the vertical aim: 1. Open the hood. See Hood Release on page 6‑15 Be placed so the headlamps are 25 ft. (7.6 m) from a light colored wall. Have all four tires on a level surface which is level all the way to the wall. Be placed so it is perpendicular to the wall. Not have any snow, ice, or mud on it. Be fully assembled and all other work stopped while headlamp aiming is being performed. Normally loaded with a full tank of fuel and one person or 160 lbs (75 kg) sitting on the driver seat. Have the tires properly inflated. Have the spare tire is in its proper location in the vehicle. 2. Locate the aim dot on the lens of the low‐beam headlamp. 3. Record the distance from the ground to the aim dot on the low‐beam headlamp. . ... . . . 6-61