GMC 2003 Sonoma Owner's Manual page 34

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Rear Seat Passengers (Crew Cab)
It's very important for rear seat passengers to buckle up!
Accident statistics show that unbelted people in the
rear seat
are
hurt more often in crashes than those who
are wearing safety belts.
To make it shorter, pull the belt, as shown until it is
snug. Buckle and position it the same way as the lap
part of the driver's safety belt. See Driver Position
on page 1-17. 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. To unlatch the
belt, just push the button on the buckle.
Don't use a child restraint on this seat. It won't work
properly.
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