Buick 2001 Century Owner's Manual page 65

5. Some vehicles have a child restraint locking feature
on the shoulder belt retractor. You can tell if your
vehicle has this feature by pulling the shoulder belt
all the way out of the retractor. Then, let the belt go
back a few inches, and try to pull the belt out again.
If you can't pull the belt out because it has locked,
it means the retractor has the child restraint locking
feature. If the belt doesn't lock and you can pull the
belt out of the retractor again, it means your vehicle
doesn't have the child restraint locking feature on the
shoulder belt retractor.
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