GMC 2009 Yukon XL Owner's Manual page 28

Manual Fold and Tumble Feature
Folding and Tumbling the Seat(s)
To fold and tumble the seat, do the following:
1. Make sure that there is nothing under, in front of, or
on the seat.
Notice: Folding a rear seat with the safety belts still
fastened may cause damage to the seat or the safety
belts. Always unbuckle the safety belts and return
them to their normal stowed position before folding a
rear seat.
2. Lift the lever, located on the outboard side of the
seat, to release the seatback.
1-22
The seatback will fold forward. Leaving the seatback
in this position creates a flat load floor.
If the seatback cannot fold flat, try moving the front
seat forward and/or put the front seatback in the
upright position.