GMC 2009 Sierra - Manual (Page 363)

7. Locate the vertical headlamp aiming screws, which
are under the hood near each headlamp assembly.
The adjustment screw can be turned with a
E8 Torx
® 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.
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