Rare M seats retrofit problem, occupancy sensor and airbag

[estupi]

Finally I bought and installed a pair of used M seats in excellent condition, electric and heated from an Individual Z4.

Everything is fine but the famous airbag light came on when connected (I took the precaution to disconnect the battery when doing the seats swap). So it seems the famous occupancy sensor problem.

I have researched a lot in the forum but can't really find how to solve the problem. I also visited the dealer for their diagnosis machine and reset the light and they couldn't. They told me there was a persistent problem in the circuit, not just the light, and because of this it could not be turned off.

Found pictures of other M seats but seems mine are different and have been modified by the previous owner. Here is a picture of the passenger seat:

I Don't see any Sensor Ocuppancy Control unit...

Detail of cable mess:

Can't even recognize which is the mat sensor cable...

This is a detail of the yellow connector:

I'm almost sure that the occupancy sensor uses pins 17, 18 and 19, since these are used in this picture and I checked they are not used in the drivers seat.

I know that people in the forum have installed >2006 seats on <2006 cars but my case is just the opposite: car is a 2008 Z4 Coupe but the seats are from a 2004 individual Z4 3.0.

I'm completely lost so any help would be really appreciated! Thanks!

 

[navid.v]

as far as I understand and read here,the pre and post facelift have different occupancy sensors,so as you say your car had a different sensor originally to the one you have installed!

have a look at this post and see what you need to do, most probably need to take the sensor out of your original seat and implant in the new one:

http://www.z4-forum.com/forum/viewtopic.php?f=2&t=23646#p331649

hope this helps.

 

[estupi]

thanks for replying! By "occupancy sensor" you mean the mat inside the leather or the occupancy control unit (black box)?

I think the solution is an occupancy bypass but I can't locate this occupancy control unit. This is the black box that was supposed to exist in my old seat (picture from left98204 post at http://www.z4-forum.com/forum/viewtopic.php?f=26&t=24819):

...but I can't see it at the bottom of the seat Anyone know if it's installed inside the seat, below the leather? All pictures I found show it outside.

 

[navid.v]

The sensor is under the cover which I think is connected to the box!

There is a bypass unit for sale by one of the members in the for sale section.

 

[Daffy]

There are 2 types of mat, one with a control box and one without. My 04 car had the boxes, my 07 car doesn't.

Where did you get the seats from? Were they from a wrecked car? If so, have a look and see if the seatbelt pre-tensioners have fired; the flexible arm will be noticeably shorter on an example which has been fired during a crash.

 

[estupi]

Thanks, I'm asking member dellboy about his bypass unit for sale. This would be the perfect solution since I don't want to strip down the leather of the seat.

Daffy, I don't know if the seats came from a wrecked car, but they didn't have seatbelts so I used the seatbelts from my old standard seats. Should be problem with this?

Since there are 2 types of mat now the question is: what to do if my seat doesn't have a control box? I suppose I need to buy one for the bypass solution, but will it work in my post facelift car which originally didn't have one?

 

[Daffy]

No, the bypass units only work on models with the control box, your car shouldn't have a control box.

The chances are that the mat is physically damaged.

A new mat is about £90 and takes about 4 hours to strip the seat and fit it yourself. Well worth doing, and no special tools required.

 

[estupi]

This would be bad news for me since I didn't want to strip the seat

So, if you have post facelift car like me (with no control box), there is no way to bypass the occupancy problem?

Besides the physically damaged mat, are there any other possible causes of the airbag light?

Thanks for the help guys! :roll:

 

[estupi]

After several weeks investigating the issue, I doubt the seat mat is damaged...

Anyone knows what is the best and cheapest way to diagnose the airbag light? I searched for Peake and other diagnosis systems but they don't work with my 2008 car...

 

[Daffy]

A local independent will do it for £20.

 

[estupi]

Hello again,

I went to an BMW dealer to have this issue checked with an official diagnosis machine and the result was error 93C1 (something like this: error 93C1: Passenger seat occupancy identification error)

So it seems the passenger mat connection, isn't it? If so, I think of these options:

- The mat is damaged
- The electronic signal of the 2004 seat is incompatible with my 2008 car.
- Other?

Am I missing something?

Thanks!

 

[PawnSacrifice]

estupi, the occupancy sensors are not compatible between the pre and post facelift cars. If you have pre-facelift seats and a facelift car then you need to change the occupancy sensor as that will be giving you the error.

If you unplug the seats without disconnecting the battery that will set of the light as well.

Given the situation that you are in my advice; strip out the sensor from the original seat, plug this into the connector under the seat, as below (swap with the existing one), without dismantling anything else for the time being, you can just tape the occupancy sensor to the back of the seat for now.

(see the link navid.v kindly provided for more info)

Take the car back to the dealer and get them to clear the airbag light - this will need resetting even if everything is fine. If everything is cool and the light doesn't come on then you know that the mat you have removed is fine (has not been damaged during removal), proved the fault was the mat and you've had the airbag light cleared. If not then you need further investigation with BMW.

Alternatively you could swap the occupancy sensor fully and take the car in to be checked by the dealer, but if you get more codes you won't be sure which stage they have come from.

Then, go home and fit that occupancy mat in the M Sport seats. Connect everything back up and you should be fine - once the battery is reconnected you shouldn't have any airbag light nonsense.

:!: Just make sure the battery is disconnected throughout.

 

[estupi]

Thank you PawnSacrifice, your help and detailed explanation are really appreciated.

The occupancy sensor and occupancy mat are integrated together in my new and older seats. I'm following your advice but instead of using my older seat mat/sensor I've ordered a new occupancy mat from the dealer, so in a week or so I'll plug it and reset the light.

If it works, then I'll fit the occupancy mat in the M Sport seats.

I'll keep updated this thread to share my experience

 

[navid.v]

just take your time when you do take the seat cover off, my fingers were sore for a few days

 

[estupi]

Hello again,

Just to thank you all of you, I completed the steps that PawnSacrifice and navid.v said and all is fully working now!

 

[navid.v]

Hello again,

Just to thank you all of you, I completed the steps that PawnSacrifice and navid.v said and all is fully working now!

brilliant so what was the issue?

 

[saseinlinie]

Hello again,

Just to thank you all of you, I completed the steps that PawnSacrifice and navid.v said and all is fully working now!

I have the same issue in my facelift Z4, is there really no way to fit an emulator in cars that don't have the occupancy mat black box ?

estupi, do you have a part number for the mat you ordered, and put it in the seat ? How much was it ?

Thanks