GMC Sierra Owners Manual
The vehicle has a visual optical headlamp aiming system. The aim of the headlamps has been preset at the factory and should need no further adjustment.
However, if the vehicle is damaged in a crash, the aim of the headlamps may be affected and adjustment may be necessary.
If oncoming vehicles flash their high beams at you, this may mean the vertical aim of the headlamps needs to be adjusted.
It is recommended that the vehicle be taken to the dealer for service if the headlamps need to be adjusted.
It is possible, however, to re-aim the headlamps as described.
The vehicle should:
Be placed so the headlamps are 7.6m (25 ft) 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.
Be loaded with a full tank of fuel and one person or 75 kg (160 lbs) sitting on the driver seat.
Have the tires properly inflated.
Have the spare tire in its proper location in the vehicle.
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 on page 10‑5
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.
4. At a wall, measure from the ground upward (A) to the recorded distance from Step 3 and mark it.
5. Draw or tape a horizontal line (B) on the wall the width of the vehicle at the height of the mark in Step 4.
Notice: Do not cover a headlamp to improve beam cut-off when aiming. Covering a headlamp may cause excessive heat build-up which may cause damage to the headlamp.
6. Turn on the low-beam headlamps and place a piece of cardboard or equivalent in front of the headlamp not being adjusted. This allows only the beam of light from the headlamp being adjusted to be seen on the flat surface.
7. Locate the vertical headlamp aiming screws, which are under the hood near each headlamp assembly.
The adjustment screw can be turned with an E8 Torxฎ socket.
8. Turn the vertical aiming screw until the headlamp beam is aimed to the horizontal tape line.
Turn it clockwise or counterclockwise to raise or lower the angle of the beam.
9. Make sure that the light from the headlamp is positioned at the bottom edge of the horizontal tape line. The lamp on the left (A) shows the correct headlamp aim. The lamp on the right (B) shows the incorrect headlamp aim.
10. Repeat Steps 7 through 9 for the opposite headlamp