DIY: e46 m3/sport coupe seats retrofit into e46 sedan

don't know if someone else has posted a DIY for this but here it goes
i have a 2001 325i without sports package
decided to get some m3 seats and swap them out
people on the forum always said they are "plug and play" and easy to swap
but i discovered a few notable issues that are worth mentioning during the swap

big shout out to valmont who did most of the work while i helped and documented the process

important - be sure to disconnect the battery as needed
and do NOT turn on your ignition before everything is connected properly and put back in place
if you turn on your car without some of the wiring connected, you may end up with an airbag warning light
turn off your car, remove the keys, and do not restart your car until you are finished



DISCLAIMER - only to be used as a reference, i am not responsible for any possible damage, injury, or death that may result as a consequence of following my posting

(this thread will be updated with more information later, such as what tools are needed/recommended. for now just putting up the pics and the basics)
recommended tools -
socket wrench and extension
16mm socket (for the seat railings)
T-50 torx screw bit for the seat belt receptacle bolt
10mm sockets for railing nuts


first step - once you acquire m3/sports seats, how do you transport them?

good news is that they fit fine in the back
just pull out the bottom seat bench (there are no screws, just tug forward and up)
and the seats fit like this
just be careful getting the seats in and out because the railings will scratch up your car body or leather easily

then you remove your old seats

the seats are held in place by 4 nuts/bolts in these 4 spots
i believe the socket you need is a 16mm?
you should have your battery connected to slide the seat forward and back to gain access to the 4 points

* you will also need to unscrew the seat belt connected to the seat rail
more on this later

be sure to have a vacuum cleaner ready because you're going to find all kinds of nasty stuff under the seats
i found 1 quarter, 4 pennies, a lot of dirt, two toothpicks, and some business cards


the seats are only connected by one group of wires, plugged in together in that yellow rectangular housing


the yellow housing is clipped onto a metal bracket under the seat
once you take out the 4 nuts and bolts holding the seat to the floor, just tilt the seat up and you should be able to see the bracket and yellow housing clearly
just pop it out gently




not sure if this step was necessary (probably is) but we lined up the rail/gear/track/whatever exactly the same on both seats
did it by using a measuring tape and marking with a sharpie
the rails contain gear and tracks ...
more on why it is important to line up your old seat railings and new seat railings in a bit

lay out the seats and just transfer the parts such as the airbag sensor(?)
you can see what each wire is hooked up to
just trace each wire, transfer everything over


here is why we thought it was necessary to line up the railings exactly the same between the sedan seats and the m3 coupe seats
the part that i am pointing to is only on the sedan seat's railing
that is the part that the sedan's seatbelt bolts onto
coupe seatbelts are bolted to the car's body, not to the seats (since passengers need more room to access the rear seats)
unless if you want to make a custom seatbelt bolt bracket or something and drill into your body, you will need to transfer this part from your sedan seat to the coupe seat

you only need to remove one railing from each seat, just to be able to attach the seatbelt

the sedan's railing with the seatbelt attachment




when you remove the railing, you can see this gear head and shaft
after you swap the sedan railing to the coupe railing (they are the exact same size/length, except that the sedan railing has the extra attachment for the seatbelt)
it is probably best if you pull up this shaft and keep the gear head in the sedan railing

like so

this is the part that gave us some trouble
the railing/shaft needs to fit in 3 places

so you need to line up the shaft to fit back into where it came from
and line up the two bolts on the railing to the holes on the 2 legs/brackets under the seat (where you took the railing off from)
one side was not lining up easily and we wrestled with it for a while
the best solution was to line up the shaft first, then line up one bolt to one hole
tighten a nut under that one bolt
and while trying to fit the 2nd bolt to the 2nd hole/leg, we took a rubber mallet and tapped it from the first side that was already inserted
(if you're doing this, you will see what i mean)

once you swap the railings with the seatbelt bracket
you need to remove and replace the seatbelt receptacle (the place where the seatbelt "clicks" into)

there is an "explosive charge" next to the seatbelt receptacle so be careful (that's to release the seatbelt after an accident)
just unscrew using the T-50 torx bit

the yellow housing and one set of wires (which trigger the explosive charge) were connected to the seatbelt receptacle

just swap over to the coupe seat

and that's pretty much it
you reverse the process to replace the seat
tighten the bolts and nuts, connect the seatbelt to the bolt on the railing

and repeat for the other side
(already have m3 steering wheel on its way, that's next mod for me)


looks a little silly having coupe seats in the sedan with the quick tilt/fold function
but why not?

some housekeeping -
it's much easier to transport and store the old seats if you slide it so that the railings are as flush as possible under the seat

you only need this one plug (pictured above) to power the seat
i did not get an error or airbag sensor light from doing this
once you get the seat railings in the desired position, just unplug
do this before you finish mounting the new seats


finished product
yes, now i need a black armrest and need to redo at least some of my interior to match better
planning on rewrapping and painting various parts

so once we had all the wires reconnected, i turned on the car and tested everything out
there was no airbag warning light
and holding down seat memory button, the carseat's memory worked right away (that is stored with the car) moving the seat and mirrors



tada~ the latest rage is putting front seats in the back
sort of look like giant booster seats

so sedan seats fit fine in the back as well, without having the benefit of the quick tilt/fold function
someone should really do a retrofit of front seats into the back (since the sedan rear seats are really uncomfortable anyway)

i just finished making this DIY at 2am ... if anything doesn't make sense or if i placed a picture in the wrong spot or something, please let me know

Nicely done!

Like those new baby seats in the back lol j/p.
Nice job on the seats and the DIY

What color is that sweatshirt?

W&M folk can do anything.

Originally Posted by XKxRome0ox

big shout out to valmont who did most of the work while i helped and documented the process

Originally Posted by CShell

W&M folk can do anything.

you mean:

Originally Posted by CShell

W&M folk can do anything.

so i hear you went to williamsburg looking for me ... too bad i moved back to california

(wait, i might be confusing you with someone else... are you the one who got hurt 4-wheeling? either way )

Subscribed thanks for the great wright up

Awesome write up. I wonder if you can delete the quick tilt. That's one thing that just looks super out of place on a sedan.

^ agreed, I wonder if e90 M3 seats would look good in there...

Nice write-up

Something worth mentioning:
Before removing the seat move the seat position, so that it is centered on the rails. This makes it easier to get out of the car, to prevent scratching the interior.
I remember keeping the battery connected right up until I went to disconnect the power to the seat, so that I could move it back and forth to gain access to the bolts.

Great DIY! Any idea if you can transfer both the inner and outer sedan seat rails to the M3 seat? I've got a chance to buy some M3 seats but the rails aren't included.

Looks awesome