GMC SIERRA CK2 1999 Owner's Manual page 14

3. Make sure the seat is secure.
The extended cab's rear seat can also be unfolded for
more seating space. To use the seat:
1. Pull the entire seat forward until it is flat.
2. Then pull forward on the RELEASE lever under the
seat cushion, on the passenger's side of the rear seat.
Push the seatback rearward until it latches.
3. After pushing the seatback upright into position, pull
the seatback forward to make sure it is locked.
1-8
2. Lift the entire seat
and push it rearward
into place.
Rear Seat (Crew Cab)
The rear seatback without a center armrest can be folded
forward to let you reach the area behind it. Your
seatback will move back and forth freely, unless you
come to a sudden stop. Then, it will lock into place.
The rear seatback with a center armrest folds forward to
let you access the area behind it.
To return the seatback to the upright position, just push
the seatback rearward until it latches. After returning the
seatback to its upright position, pull the seatback
forward to make sure it is locked.
To fold a seatback forward,
pull this lever forward and
fold the seatback forward.
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