Cadillac 2010 DTS Owner's Manual page 362

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) the width of the
vehicle at the wall where it was marked 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 aimed. This should allow only
the beam of light from the headlamp being
aimed to be seen on the flat surface.
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7. Locate the vertical headlamp aiming screws. They
are located under the hood near each headlamp
assembly. First lift the flap to access either of them.
Each one is the top outboard screw by the " V" on the
cover panel next to the aiming flap.
The adjustment screw can be turned with a 6 mm
hex wrench.
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.
The top edge of the cut-off should be positioned at
the bottom edge of the horizontal tape line.