GMC 2009 Sierra - Manual (Page 26)

Q:
What is wrong with this?
A:
The belt is behind the body.
{ CAUTION:
You can be seriously injured by not wearing
the lap-shoulder belt properly. In a crash, you
would not be restrained by the shoulder belt.
Your body could move too far forward
increasing the chance of head and neck injury.
You might also slide under the lap belt. The
belt force would then be applied right on the
abdomen. That could cause serious or fatal
injuries. The shoulder belt should go over the
shoulder and across the chest.
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