GMC 2001 Sierra 1500 Pickup Owner's Manual page 23

Rear Seat (Extended Cab)
Folding the Rear Seat
The extended cab's rear seat can be folded up to provide
more cargo space. To fold the seat:
2. Fold the seat cushion upward until it latches with
the seatback.
1-10
1. Pull forward on
the release strap
located under the
rear seat cushion.
The extended cab's rear seat can also be folded open for
more seating space. To use the seat:
1. Push rearward on the seat cushion while pulling up
on the release strap under the seat cushion. Pull the
seat cushion downward until it latches.
2. After pulling the seat cushion down, pull up on it to
make sure it is locked.
3. Push and pull on the
seat to make sure the
seat is secure.