Buick 2004 LeSabre Owner's Manual page 286

If your vehicle is damaged in an accident, the headlamp
aim may be affected. Aim adjustment to the low beam
may be necessary if it is difficult to see lane markers (for
horizontal aim), or if oncoming drivers flash their high
beams at you (for vertical aim). If you believe your
headlamps need to be re-aimed, we recommend that
you take your vehicle to your dealer for service.
However, it is possible for you to re-aim your headlamps
as described in the following procedure.
Notice: To make sure your headlamps are aimed
properly, read all the instructions before beginning.
Failure to follow these instructions could cause
damage to headlamp parts.
The vehicle should be properly prepared as follows:
•
The vehicle should be placed so the headlamps are
25 ft (7.6 m) from a light colored wall or other flat
surface.
•
The vehicle must have all four tires on a perfectly
level surface which is level all the way to the wall
or other flat surface.
5-48
•
The vehicle should be placed so it is perpendicular
to the wall or other flat surface.
•
The vehicle should not have any snow, ice or mud
attached to it.
•
The vehicle should be fully assembled and all other
work stopped while headlamp aiming is being done.
•
The vehicle should be normally loaded with a
full tank of fuel and one person or 160 lbs (75 kg) on
the driver's seat.
•
Tires should be properly inflated.
Headlamp aiming is done with the vehicle low-beam
lamps. The high-beam lamps will be correctly aimed if
the low-beam lamps are aimed properly.