Chevrolet 2003 Impala Owner's Manual page 24

Shoulder Belt Height Adjuster
Before you begin to drive, move the shoulder belt
adjuster to the height that is right for you.
To move it down, squeeze the release lever and the
shoulder belt guide as shown and move the height
adjuster to the desired position. You can move
the adjuster up just by pushing up on the shoulder belt
guide. After you move the adjuster to where you
want it, try to move it down without squeezing the
release lever to make sure it has locked into position.
Adjust the height so that the shoulder portion of the belt
is centered on your shoulder. The belt should be
away from your face and neck, but not falling off your
shoulder.
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