GMC Yukon Denali 2006 Manual page 48

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 1-47.
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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