BMW Z3 M Sport Heated Seat Base Repair
Article Submitted by Gookah

On our recently purchased Z3, and found that the seat base on the drivers side would not heat up, whether on low or high heat, the car had the M-Sport seats. So today I carried out the following investigation.

Firstly I removed the seat. Take the key out of the ignition so no airbag issues…
Move the seat forward and remove two rear bolts from the runners with a 16mm socket, and the lower seat belt anchor with a 16mm spanner.

Move the seat backwards and remove two nuts from the runners with a 13mm socket.

Tilt the seat to one side and you will see the yellow connector underneath:

the black retainer slides outwards to the right as pictured:

this releases the connector:

now you can carefully take the seat out completely.

Start by removing the side plastics. One screw here:

one by the tilt lever:

and one at the front of the seat:

then unclip and pull back the fabric flap at the back of the seat:

remove the side flaps by removing the retainer clip:

Now to start unhooking the seat fabric, I bent the small tags out wards to aid removal:

Then I cut the brown and the white wires at the back of the seat base to allow the seat cushion to be removed completely from the frame.

Then I started to peel back the leather to expose the hog rings, which pull apart with some long-nose pliers.These hold the leather to the seat bars underneath. There are three of them at the front of the seat

and this then exposes the problem:

A burnt and broken wire.

I assume that as the car does not have an electric roof, it was caused by someone kneeling on the seat, probably breaking some of the wire strands causing it to overheat and burn out.

So to effect a repair, I decided to splice another wire in between, to get rid of damaged bits and to allow a better routing of the wire.
So solder two joints and heat shrink:

Cut into the foam so it can be sunk and protected:

and the finished repair:

Continuity tried at the cut wires after adding some bullet connectors and joined up before re-assembly:

Reversal of the above to refit:

bend the hog rings and stitch them back on with the pliers:

Hoover the carpet, places you can’t get to normally:

and refit the seat:
Switched on, no airbag light, and a fully working seat heater.
Didn’t cost a penny, in fact I made 52p…

One thing I noticed whist the cover was off, is the reason for the seat bolster being flat:

the foam had parted and no longer held its shape, so a bit of duck tape:

It’s not pretty but it does the job perfectly.