So I was correct it errs on the side of caution. If butt sensor is unknown the bag fires as occupied. You should be able to deactivate the sensor in software but the cheater resistor is a good workaround. The stage of ignition is based on impact not weight on the seat


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Interesting, yup we can get the Seat Occ Bypass or Fakey Plug in the UK for about £10 :) OR! I can dismantle the one off the bottom of the seat, seems I can trick the with a couple of resistors and diode as the sensor really just sends a constant current to ECU to tell it, hey I am okay. Hmm... I am alright with electrics, perhaps I will solder a couple of 200 ohms resistors ether side of a low diode (never liked bridging resistors even if it makes for a more 'efficient circuit!') and close the circuit inside the Seat Occ sensor box. That way it will LOOK OEM, I can attach the cable so it not hanging loose (incase of sneeky MOT inspectors) and it will not throw and error.

Interesting, anyone done this? if not I will take a photo. Yes, I am trying to save £10 but... really, its a little project and I enjoy electronics, if I fix it for 1 hr time and a 50p couple of diodes/resistors I will be very happy. :D

I have a thought/question...not a judgement...but if you trick/disable the occupancy mat sensor to think that no one is in the seat...what happens if you have a front passenger and you get involved in a frontal or passenger side accident?

How will the air bags deploy (if at all if it thinks no one is in the seat)? What are the results of the occupancy sensor being deactivated and how does it affect that front seat passenger? Whereas, if the sensor is defective and illuminated...it will assume someone is ALWAYS in the seat...thus deploy. Just curious as to what you say to the possibly injured front passenger....and God forbid...what do you say to the family if the injury is fatal? :dunno:

Occupancy Sensor and SRS Light
 

The sensor emulator is tricking the computer to think there is always somebody in the seat

The trade-off is that the airbag will go off and waste the airbag even if nobody is in the seat.

:thumbup: Got it...I wasn't sure if the emulator did what you wrote above...or if it simulated that no one was in the seat. I can live with the first, not the latter...as well as my front seat passenger. :D

Smart word play "your passenger can live with it" quite literally could be the case. The chart above shows that even in the case of a defective or missing butt sensor the airbag will deploy. It's the only logical answer. Imagine when a passenger dies because the connector was dirty on the butt sensor!


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In the 5-series E39, people often use the "Seat simulator". Go to ebay and search "e39 seat simulator", you will see some listed for $15.

I installed this seat simulator in my E39 (1998 528i) about 10 years ago.

You can go to bimmerfest to see the pros and cons. I personally don't care for this BMW gimmick as many cars out there do not have this gimmick. Glad to get rid of the this gimmick using a seat simulator.

My friend had his butt sensor replaced for $450 on his vw Passat. I googled options and found the emulator for $10 and knew immediately that was the way to go.

If you can disable the seatbelt alarm you wouldn't have to keep the seat belt latched without a passenger I logically assume you would have to otherwise since the computer sees the seat occupied


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Hi Andrew, I might be wrong in this so will have to check but the way I think it works is this.

1 - Car unlocks
2 - Doors open, interior lights open and ECU registers open doors.
3 - On open door register, then ECU asks question on occupancy on seat.

For example, I have opened the passenger door and put a heavy box on the seat and the seat belt light has come on. If I get in the drivers door and pass the same heavy box over and put it on the seat, the seat belt light stays off.

Again, this could be just because I have a faulty seat occupancy sensor rather than the process checks of the ECU but once I bypass the Seat Occ sensor I am about to find out if I am going to get the annoying seat belt warning noise.

:)

I have a 2006 3.0i and I've also had the seatmat problem. Sometime it worked, sometime it did not recognize a adult person...so I decided to get rid of the seatmat. Replacing it at the dealer would have costed around 1000$...that's not a option in my eye.

The 2006 X5 would have been covered by a recall in USA..but as I'm living in Italy, no coverage at all.

The latest X5 E53 models (2005-2006) and respective seatmats, don't use a simple signal that you can reproduce with some resistors. It's a digital signal you have to reproduce with the help of a microprocessor.

I've found digital seatmat emulators on the bay...and used one for about 1 year. It did the job...but actually it caused other problems like sometimes the remote key not beeing able to lock the car or "key in ignition" ringing even if the key was not in the ignition. As soon as i disconnected the emulator..."key in ignition" message disappeared. Found the culprit!

I then bought another module, hoping that maybe this would behave differently. Installed it, no more strange behaviours...but unfortunately it drained the battery over night.

It seems that even if those emulators are able to get rid of the seatmat, they are not comunicating with the other modules as it should...

I ended up coding the occupancy sensor out with the help of BMW SCANNER...by unchecking "Occupancy classification System" and "Seat Occupancy Recognition" in the Airbag module.

It did the trick, but actually now also the seatbelt warning is not working, even if I did non disable it in BMW Scanner. I guess The Occupancy Classification System is needed for the seatbelt warnings to be active.... but it's just a guess.

I hope to be able to read the Airbag module with NCS EXPERT in future, to see what unchecking of the "Occupancy classification system" and "Seat Occupancy Recognition" actually did on the coding of the car... but at the moment I am not familiar with it.