GMC 2009 Yukon XL Owner's Manual page 27

Reclining Seatbacks
To recline the seatback, do the following:
1. Lift the lever located on the outboard side of
the seat.
2. Move the seatback to the desired position, then
release the lever to lock the seatback in place.
3. Push and pull on the seatback to make sure it is
locked.
To return the seatback to an upright position, do the
following:
1. Lift the lever fully without applying pressure to the
seatback and the seatback will return to the upright
position.
CAUTION:
{
If either seatback is not locked, it could move
forward in a sudden stop or crash. That could
cause injury to the person sitting there. Always
push and pull on the seatbacks to be sure they
are locked.
2. Push and pull on the seatback to make sure it is
locked.
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