2007 GMC Yukon Owner's Manual - Page 56

The safety belt locks if there is a sudden stop or a crash, or if you pull the belt very quickly out of the retractor. {CAUTION: You can be seriously hurt if your shoulder belt is too loose. In a crash, you would move forward too much, which could increase injury. The shoulder belt should fit against your body. To unlatch the belt, push the button on the buckle. Rear Safety Belt Comfort Guides Rear shoulder belt comfort guides may provide added safety belt comfort for older children who have outgrown booster seats and for some adults. When installed on a shoulder belt, the comfort guide positions the belt away from the neck and head. 56