Chevrolet Suburban 2007 Owner's Manual page 54

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 on page 59.
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 up on the
shoulder part.
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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 would 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.