[CP911]

Hello all,

In a last-ditch effort to retain the factory passenger seat occupancy/airbag functionality in my M240i with custom bucket seats, I purchased an e92 occupancy sensor from ECS Tuning and had it shipped to the UK where the seats are being made. The plan was to have them insert the sensor under the passenger seat upholstery and then pray I can somehow wire things up to work properly. Now, I'm having second thoughts, and instead, I'm considering sacrificing my stock passenger seat's Dakota leather cushion cover (a $600 replacement part which contains the 2-series occupancy sensor within) in order to pull out the sensor and send it to the UK.

Can the e92 sensor be wired in to work properly? Anyone know how these seat occupancy sensors actually output their signal? I'm guessing they have a 12V power and a ground connection, along with a 0V/5V output aka "high" or "low" output logic. If so, then I'm sure I can wire it up to work. However, if it's more complex than that, or if things have changed for the latest F-generation, I'd like to know so I can adjust my plan accordingly.

I realize this isn't knowledge that just anyone has readily available, but hoping maybe a BMW tech or engineer actually knows how these work and can give me some advice on how to proceed.

I'm aware of the seat occupancy and seatbelt emulator resistors, but I'm trying to avoid going down that path if possible for liability reasons e.g. if I decide to take a 12-year old kid or Grandma for a ride on the street and the airbag deploys and takes their head off. If you can change my mind or show me the logic that would suggest this is the best way to go, then I'm all ears.

Thanks for listening and for any advice you may be able to provide!

Cheers!

[Maynard]

I think that the systems are different for USA and ROW, with a simpler pressure switch used overseas. Try hunting around here to see if it gives you any additional ideas https://www.newtis.info/tisv2/a/en/f...ch?q=occupancy

[CP911]

Maynard, sir, you are the man! Newtis.com is my go-to for DIY maintenance, but never thought to explore it for wiring diagrams or functional descriptions regarding the passenger occupancy sensor. It's all there. Genius!

To my amazement, the European and US passenger airbag functionality is vastly different. Straight from the horse's mouth:

For F22 M240i:

Front passenger seat occupancy detection (Europe version):
The front passenger seat occupancy detection comprises a seat occupancy mat with conductor paths and pressure sensors. The resistance value of the pressure sensors is read in and evaluated in the Crash Safety Module (ACSM) (ACSM stands for "Advanced Crash Safety Module", hereinafter "Crash Safety Module").

The seat-occupancy detector is only used for the seat belt warning. If the seat occupancy mat detection indicates that the front passenger seat is occupied, the passenger belt must also be inserted in the belt buckle. The seat belt warning then goes out. If the crash safety module triggers the airbags, the corresponding airbags on the passenger's side are also triggered even if the front passenger seat is unoccupied.

Functional description
When a weight is placed on the seat, resistance in the seat occupancy mat changes. The seat is detected as not occupied up to a weight of approximately 12 kg (only applies if the seat-occupancy mat is installed between the cover and the foam insert of the seat). The seat occupancy detection function, however, also depends on the type of seat. e.g.: The material tension in a leather seat or a taut sports seat is already interpreted as pressure on the sensors. In such cases, a weight below 12 kg can trigger the "seat occupied" condition.

The resistance value is transmitted to the Crash Safety Module (ACSM) in a direct wire. For example, if the passenger's seat is recognised as being occupied without the seat belt buckle switch sending a signal, a fasten belt warning will be emitted by the Crash Safety Module.

************************************************** ************************************************** *************

Seat occupancy detector, front passenger (US version):
In accordance with the stipulations of the National Highway Traffic Safety Administration (NHTSA) a small child in a child restraint system on the front passenger seat must be automatically detected. Upon detection, the airbags on the passenger's side are automatically deactivated (front passenger airbag, side airbag, knee airbag). The indicator light for front passenger airbag deactivation lights up.

Functional description
The front passenger seat occupancy detection consists of a seat occupancy mat with a capacitive sensor system and evaluation electronics. The occupancy of the front passenger seat is detected by measuring the capacitive resistance of the human body.

The electronic evaluation unit picks up the change and determines the corresponding status.

The airbags on the passenger's side (front passenger airbag, side airbag, knee airbag) are deactivated automatically when the seat is empty or a small child is detected in the child restraint system provided for this purpose. The indicator light for front passenger airbag deactivation lights up.

If a person of adequate size sitting correctly is detected, the airbags on the passenger's side are activated. The indicator light for the front passenger airbag deactivation does not light up.

The front passenger airbag could deactivate with a youth or adult seated in certain positions (indicator light for passenger airbag deactivation comes on). In these cases, the seat position must be changed until the indicator light for the front passenger airbag deactivation goes out (airbags on the passenger's side are activated).

Notice!

Electronic devices that are placed on the front passenger seat, e.g. laptop computers, mobile phones etc., could cause the front passenger airbag to activate.

This behaviour occurs primarily with devices that are connected to the vehicle electrical system via a USB cable or other charger adapter.

In vehicles with an acoustic seat belt warning, this could cause the warning signal to sound.

Moisture on the seat surface can also cause a faulty seat occupancy detection.

The evaluation electronics transmit status information to the Crash Safety Module (ACSM) in cyclical transmissions. Potential fault statuses are stored in the Crash Safety Module's (ACSM) fault memory.

If the seat occupancy mat is defective, the airbags on the passenger's side are automatically disabled (front passenger airbag, knee airbag, side airbag). The indicator light for front passenger airbag deactivation lights up.

Failure of the component:
If the front passenger seat occupancy mat fails, the following behaviour is to be expected:
Fault entry in the crash safety module (ACSM)
Airbag warning lamp lights up
Indicator lamp for front passenger airbag deactivation (only for US version)
Airbags on the passenger's side are automatically deactivated (front passenger airbag, side airbag, knee airbag)

[CP911]

In summary, my fears of airbag deployment with a smaller child or elderly person are completely unwarranted in a US vehicle. All of the passenger airbags are DEACTIVATED by default if there is a sensor failure or presumably if there is no sensor in place at all.

It seems the only liability I would have if I install the bucket seats without a sensor is that there would be NO passenger airbag deployment at all under any circumstances. Since a child would not be at risk, I am slightly more comfortable with this, but an adult could be at risk without airbag deployment in normal street driving. On track, with an instructor wearing a helmet and with a harness, I'm guessing it is probably preferred to not have airbags going off in a crash anyways.

Additionally, a deeper look at the M240i wiring diagrams and e92 wiring diagrams suggest that the e92 sensor would NOT be compatible.

The only thing that was not addressed by the functional description of the passenger occupancy sensor for US vehicles is how the seatbelt warning light and corresponding audible chime is related. I'm assuming that like the much simpler European functionality, it would chime and warn me that the passenger belt is not on once the US-spec's capacitive sensor detects a "person of adequate size" sitting in the seat. I'm pretty sure a seatbelt emulator resistor would take care of this problem with the caveat that the system would always think the passenger is wearing their seatbelt even if he or she is not. Another potential liability, but I will just have to make sure my passengers always wear their seatbelt.

I would have the airbag light on my dash, which kind of sucks, but not a big deal in the end.

Aside from my conclusion that adults will not have airbag deployment in a street accident, does anyone see any other potential concerns or liabilities if I proceed with this bucket seat install sans occupancy sensor???

[CP911]

Another observation/conclusion: The European functionality is much more aftermarket seat-friendly. The seat sensor only affects the seatbelt warning/chime, so you can simply install a seatbelt emulator resistor and call it a day. Airbags are designed to deploy no matter what (good for adults during street driving), but it looks like you can manually disable them (according to the BMW TIS) via a "switch" function within the ISTA software for specific scenarios like track driving or installing a child safety seat in the front passenger seat.

I didn't even know child safety seats can be legally installed in a front passenger seat, but apparently so as long as you manually deactivate the airbags (in Europe) or, according to the NHTSA here in the US, have an automatic detection sensor to deactivate them for you. Found that very surprising and interesting...

[ghostrider1969]

I found a set of seats comfort used but in excellent condition to replace those basic semielectric of my F10 530dx. Mine was built in September 2011 and the donor car was 2010. However, in September 2011 BMW changed the airbag control unit and started to mount a different type of front passenger presence sensor. In particular, until August 2011, the control unit was of the type with three connectors and the sensor that interests us here had three cables, positive, mass and data bus (LIN), while from September 2011 ca centralina becomes two connectors (of which one maxi, with pinout more or less corresponding to the previous control unit) and the sensor becomes of the type to two cables, positive and mass. Well, still remaining the fact that I could disassemble from my new sensor and mount it on the comfort seat (option that I would like to leave as a last resort because the operation would be quite mangy) I was looking for a way to digest the three-wire sensor in my control unit. In particular, on etk I noticed that the newest sensors are data as backwards compatible... Moreover, comparing the electrical diagrams of the version - and + 09.2011 I noticed that the cables have the same colors, even if the pinout of the new control unit changes and if in the version + 09.2011 the LIN connection disappears. In your opinion, can I use the three-wire sensor simply by omitting to connect the LIN cable or otherwise? Thank you