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Thread: Air bag light on a E31 - 1995 BMW 840ci Driver Seat

                  
   
  1. #1

    Air bag light on a E31 - 1995 BMW 840ci Driver Seat

    SRS light is on. The dealer recommends changing the seat! $1500+. Each time the error code is reset, the SRS light and error code comes back after 3 days.

    I am not a car mechanic but it seems that airbag sensor does not think anyone is sitting on the seat. My basic electrical knowledge tells me that if the wires can be located may be they can be hard wired to be on or a resistor can be inserted to show teh correct resistance to the sensor.

    I would appreciate any help in exchange for beer, pizza, and my elbow grease. If there is a seat belt sensor that can also be a possible problem spot.

  2. #2
    Senior Member mcoupemindy's Avatar
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    I've never worked on an 840, however I have made lots of resistor packs for our cars.

    Does the passenger seat have the same type of sensor? If so, I'd just read the resistance with weight in the seat and no-one in the seat, and create a resistor pack. Might take some creativity however would completely avoid the seat replacement.
    Jonathan Thayer - jonathan.michael.thayer@gmail.com
    '99 Imola Red M Coupe, '08 Interlagos Blue Z4M Coupe

  3. #3
    That makes sense in terms of what the system expects to see as on/off states. How much time does it tale to find the wires on the other seats you have worked on? I think the 840 seats should have similar construct.

  4. #4
    Senior Member mcoupemindy's Avatar
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    The easiest way is to find an ETM (Electrical Troubleshoot Manual) and look at the seat wiring - this will help find the circuit on the seat connector. If you don't have this, you'll just need to rule out any other circuits going to the seat with a multimeter. In addition, if I remember correctly, the seat sensors in many BMW's are very small gauge wire compared to the electric motors, etc.

    I hope this information helps you out a bit!
    Jonathan Thayer - jonathan.michael.thayer@gmail.com
    '99 Imola Red M Coupe, '08 Interlagos Blue Z4M Coupe

  5. #5
    Senior Member John in VA's Avatar
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    John in VA

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  6. #6
    Wow. Thanks very much.

  7. #7
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    The dealer said to replace the seat? What an idiot. The GT1 or MODEC or whatever they use now would tell them what the problem is and fixing it isn't that hard. I don't think there is a occupancy sensor in the drivers seat. Seems pointless to me. I mean, the car is on and running, wouldn't there be a driver?

    Anyway, Most of the SRS codes I've seen are a result of a faulty seat belt receptacle, passenger side occupancy mat, and broken wires on the slip ring.

    If you want to come out my way, (Eldersburg, Md) I'll hook up the GT1 and see what the probelm really is.
    No matter where you go, there you are!

  8. #8
    Quote Originally Posted by rrsperry View Post
    The dealer said to replace the seat? What an idiot. The GT1 or MODEC or whatever they use now would tell them what the problem is and fixing it isn't that hard. I don't think there is a occupancy sensor in the drivers seat. Seems pointless to me. I mean, the car is on and running, wouldn't there be a driver?

    Anyway, Most of the SRS codes I've seen are a result of a faulty seat belt receptacle, passenger side occupancy mat, and broken wires on the slip ring.

    If you want to come out my way, (Eldersburg, Md) I'll hook up the GT1 and see what the probelm really is.
    Thanks for the offer and I will take you up on it and schedule a time. I agree on the SRS. I think it should be armed as soon as the car turned on. I love our Bavarian engineers. I see some of the over-lord thinking on my BMW motorcycle as well. It will be great to know if is a seat belt receptacle! PM sent.

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