my 2002 grand cherokee drivers seat, has every function working, but one. It will not go forward or back. WHY ??????

 

Probably the motor, or the switch died. Since it is affecting both front, and rear movement I would say it's probably the motor. I had to replace the front motor recently. Yes you can replace the motors, but you have to find a donor seatbase. It is just a matter of knocking out pins, and removing clips. But I would check the switch before going out and messing with the seat motors.

 

It could also be the drive cables, you really have to pull the seat and see whats going on.