Buick 2003 Century Owner's Manual page 33

The safety belt locks if there's a sudden stop
or
a crash,
or if you pull the belt very quickly out of the retractor.
You can be seriously hurt if your shoulder belt
is too loose. In a crash, you would move
forward too much, which could increase injury.
The shoulder belt should fit against your body.
I
I
To unlatch the belt, just push the button on the buckle.
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