GMC Yukon Denalid Owner's Manual page 54

2. Push the latch plate into the buckle until it
clicks.
Pull up on the latch plate to make sure it is
secure.
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 60.
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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