GMC Yukon Denalid Owner's Manual page 474

To adjust the vertical aim, do the following:
1. Open the hood. See Hood Release on
page 429 for more information.
2. Locate the aim dot on the lens of the
low-beam headlamp.
3. Measure the distance from the ground to
the aim dot on the low-beam headlamp.
Record the distance.
474
4. At the wall or other flat surface, 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
or flat surface 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.