Chevrolet 2004 Impala Owner's Manual page 32

1. Pick up the latch plate and pull the belt across you.
Don't let it get twisted.
The shoulder belt may lock if you pull the belt
across you very quickly. If this happens, let the belt
go back slightly to unlock it. Then pull the belt
across you more slowly.
2. Push the latch plate into the buckle until it clicks.
Pull up on the latch plate to make sure it is secure.
1-26
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 1-30. Make sure
the release button on the buckle is positioned so
that you would be able to unbuckle the safety
belt quickly if you ever had to.
3. To make the lap part tight, pull down on the buckle
end of the belt as you pull up on the shoulder part.