GMC 2002 Savana Van Owner's Manual page 42

When the shoulder belt is pulled out all the way,
it will lock. If it does, let it go back all the way
and start again.
If the belt is not long enough, see "Safety Belt
Extender" at the end of this section.
Make sure the release button on the buckle is
positioned so you would be able to unbuckle the
safety belt quickly if you ever had to.
3. To make the lap part tight, pull down on the buckle
end of the belt as you pull up on the shoulder part.
The lap part of the belt should be worn low and snug on
the hips, just touching the thighs. In a crash, this applies
force to the strong pelvic bones. And you'd be less likely
to slide under the lap belt. If you slid under it, the belt
would apply force at your abdomen. This could cause
serious or even fatal injuries. The shoulder belt should
go over the shoulder and across the chest. These parts
of the body are best able to take belt restraining forces.
The safety belt locks if there's a sudden stop or a crash.
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