Are you out of warranty?
Usually, the problem is a jammed drive mechanism due to presence of foreign object (coins, pens, etc). But could also be with the switch, harness or related motor. Refer to the link below, page SE-11 for info about Auto Drive Positioner, SE-39 for diagnosis, SE-81 to 84 for wiring diagram and SE-96 for Seat Assembly.
http://www.nicoclub.com/FSM/ma...e.pdf