How do i get the front hinge off my R90/6 BMW seat?

Open tool box, at rear of seat, with key and unhook or unbolt the seat from inside tool box.

Pull lever on right or left side, up under the seat. It can also be at the rear of the seat, right or left side, again up under the seat. Lift seat off up and to the rear. Sometimes it's hooked on both sides with a rod or cable connecting both sides. These can break. Make sure both are unhooking.

Same as above only you use a key.

Remove the two bolts on either side at the rear of the seat. Pull seat to rear.

Nuts or bolts, at the rear and below seat, under the rear fender Remove bolts holding down the rear seat . Remove seat and then remove two bolts, at the rear, holding the front seat on.

Unlock lever on side of seat. Seat then pivots on two hinges to open. Can open to the right or left. Might have no lock.

Push button on side. Left side, I haven't found a push button on the right side... yet ! Can be locked or unlocked with a key.

Pull lever at front of seat, right or left side. Seat lifts up with the hinge at the rear.

Pull lever at rear of seat, right or left side. Seat lifts up with hinge at front.

Pull lever at front of seat, right or left, and whole seat comes off. Seat has pegs underneath that fit into rubber grommets on the frame.

This is either an electrical problem or the infamous twisted seat problem caused by the cables between the motors and reclining gear units of the power seat.
Check the connector under the front of the seat and make sure it has not been disconnected
listen to determine whether the motor at the front of the seat are turning when you try to move the seat (they are fairly quiet)
If the motor spins, then search internet for "bmw twisted seat"
good luck

after removing the front seat the back seat lifts up from the rear and then is removed by pulling it backwards

The hinges and bumpers on plastic seats are not replaceable. The bumpers are molded in and the hinges are installed with special tools while the plastic is still warm.
Sorry but that's way Bemis does things and is way most good Plumbing shops will not buy or sell them.
They were not like that untill they started having their seats made in China however this may help you http://www.bing.com/shopping/search?q=bemis+toilet+seat+replacement+parts&FORM=HURE


http://www.bizrate.com/plumbing-supplies/oid1620858646.html

The location of the battery in the BMW 525i series is under the back seat on the passengers side. To access the battery, grab under the front portion of the back seat and pull upward with some force. There are two slips into which the seat is secured. One on the passenger side and one on the drivers side, again in the front of the back seat. There is not one in the center.

Passenger side.... early 2006 model.
pull up on the front of the cushion to get the seat pad off.

Late 2006 model in trunk passenger side of spare tire well.
Underneath trunk lining carpet.

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There is 4 bolts under the seat. 2 in the front and 2 in the back remove them and the seat should come right out.