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Thread: Bypass Seat Occupancy sensor

  1. #1
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    Bypass Seat Occupancy sensor (SOLVED)

    My airbag light came on a couple of month ago. After doing a OBD check using INPA i see that my occupancy mat give me this issue.

    After doing some research i found our that we can bypass this sensor.
    So I bought some resistors and diode and started to build this mod.

    First attempt was using 2 100ohm resistors and a 1N4007 diode. al three parts i connected to the cables coming out of the board os the sensor. Cathode side was soldered to the blue cable.
    Used next drawing to do this:

    P1080380s.jpg

    And this is how I did it:

    IMG_20181114_164002.jpg

    After that i put everything back in to the case (wanted the oem look), and installed under the seat. Unfortunately I was not able to clear my error code. Not with INPA and also not with PA Soft 1.4

    If I look at the live data inside INPA i see next message:

    IMG_20181116_165713.jpg

    Passenger Seat DOT is white , which means system does not see any passenger, so airbag will work if an accident happens.
    Unfortunately light still on.

    After this I got a second sensor from the scrap yard and used a different source. This mod uses 1 4.7K resistor and 1 1N4007 diode.
    Found it in next youtube video:



    And this is how I did it:

    IMG_20181116_161045.jpg
    IMG_20181116_161821.jpg

    Again I put everything back into the sensor case, and attached to the seat connector (with connector of sensor to the cable under the seat)
    After this i wanted to clear the code, but unfortunately system refuses.
    Both INPA and PA Soft 1.4 will not to the job.

    And again, i I look in INPA live data I see same as before. A white dot next to passenger seat.

    I have no idea why i am not able to clear the error.
    To be sure that I did everything right I disconnected my modified sensor, and run again INPA live data.
    And strange to see that without a sensor attached i again get a WHITE dot next to passenger seat.

    INPA gives me next message when i want to clear this error:

    ApiCheckJobStatus: Job-Status error: [ERROR-ECU-REJECTED] instead of [OKAY] Continue script processing?

    After clicking YES, I get message ERROR CLEAR. But light wont go away , and error stays

    Hope somebody have any idea what i am doing wrong.
    Last edited by seninnha; 11-20-2018 at 10:28 AM.

  2. #2
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    I found that the connectors on the sensor can get gummed up(?). I demated and mated them, and cleared the code with the Peake R5 SRS scan tool. Never came back, after many years.


    Ed in San Jose '97 540i 6 speed aspensilber over aubergine leather. Build date 3/97. Golden Gate Chapter BMW CCA Nr 62319.

  3. #3
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    I get that you can bypass the sensor, but why would you want to?

  4. #4
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    Shade-tree fix.


    Ed in San Jose '97 540i 6 speed aspensilber over aubergine leather. Build date 3/97. Golden Gate Chapter BMW CCA Nr 62319.

  5. #5
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    Quote Originally Posted by makenzie71 View Post
    I get that you can bypass the sensor, but why would you want to?
    Reason to bypass the sensor is because my airbag light is on, and this is due to a bad occupancy passenger mat. (which only is needed if person sitting next to you is less them 40 pounds)

    @edjack:

    what do you man by Shade-tree fix?
    Last edited by seninnha; 11-19-2018 at 05:46 AM.

  6. #6
    geargrinder's Avatar
    geargrinder is offline Having No Trouble Here BMW CCA Member
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    Is your hack assembly (the resistor and diode) maybe shorting out to some other connection when you squeeze it in the box? Standard procedure for me in projects like this is to plug the thing in unassembled temporarily to test it before putting it all back together in the car..l make sure it works before reassembling all the bits.

    Also theres a possibility that the flaw is not the sensor mat itself but is the module aka the control box you are hacking around with. Maybe that is the bad part and not the switch itself.
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  7. #7
    geargrinder's Avatar
    geargrinder is offline Having No Trouble Here BMW CCA Member
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    “Shade tree mechanic” generally means an amateur not real good mechanic that only has limited technical understanding, likely misdiagnoses because of poor knowledge or misapplying some erroneous “common knowledge” (example - always saying a vibration on highway is “probably warped rotors!”), and likes to take cheap and quick shortcuts instead of doing things the right way. The idea is that he’s some guy down the street who doesn’t even have a garage but just works on the dirt under the shade of a tree in his yard.
    2003 M3CicM6 TiAg
    2002 540iT Sport Vortech S/C 6MT LSD TiAg
    2008 Audi A3 2.0T DSG (the daily beater)
    2014 BMW X1 xDrive28i (wifemobile)

    Former:

    1985 MB Euro graymarket 300SL
    1995.5 Audi S6 Avant (utility/winter billetturbobattlewagen)


  8. #8
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    Quote Originally Posted by geargrinder View Post
    “Shade tree mechanic” generally means an amateur not real good mechanic that only has limited technical understanding, likely misdiagnoses because of poor knowledge or misapplying some erroneous “common knowledge” (example - always saying a vibration on highway is “probably warped rotors!”), and likes to take cheap and quick shortcuts instead of doing things the right way. The idea is that he’s some guy down the street who doesn’t even have a garage but just works on the dirt under the shade of a tree in his yard.




    Ok thanks for explanation.
    But don't worry, have enough experience working on cars.
    And what I don't now, I search. And if still not able to understand or find, then I ask.

    That the good thing about having a forum.

    it's a shame that some people think your a noob for asking. Wonder if they where born with all their knowledge

    About the sensor. I have a third sensor. Will try that one in the car without any mod.
    I know for sure that diode and resistor are NOT shorting out.
    First one I made where covered with a sleeve, and second one with hot glue.
    Last edited by seninnha; 11-19-2018 at 11:28 AM.

  9. #9
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    Why not fix it right and stop hacking the car all up?
    Set the controls for the heart of the sun

  10. #10
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    See post #4.


    Ed in San Jose '97 540i 6 speed aspensilber over aubergine leather. Build date 3/97. Golden Gate Chapter BMW CCA Nr 62319.

  11. #11
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    Maybe some people can't afford the $1800.00 it takes to put in a new sensor in!

  12. #12
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    Don't worry JetBlackJack. I think that some people, are not aware that not everybody , specially here in Europe, is able or wants to empty his credit card for new parts.
    That is why we have a big industry in second had parts. And for those parts that are not available we need to find other solutions. And this hack was mine solution (and as far as I can read online, i am not the only one)

  13. #13
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    So now that you’ve hacked your car all up, and you have a passenger in the passenger seat, and an occurrence comes up where the airbag should be needed, could have saved the passenger, but no, you didn’t want to bother fixing the issue properly, hope you can live with that, face yourself, or their loved ones. I hope it doesn’t come to that.
    Last edited by BimmrMeUpSnotty; 07-08-2019 at 01:13 PM.
    Set the controls for the heart of the sun

  14. #14
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    I don't think that's the result.

    When the sensor is working it DISARMS the passenger airbag when it detects no passenger, or a passenger under 40lbs (i.e a little kid/baby, for whom the airbag could do more harm than good).

    So if you bypass it, the passenger airbag is always ARMED. Meaning, it will always deploy.

    (I have done this mod on my car using a $10 ebay dongle).

  15. #15
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    Ok, so..... now, if a kid is riding shotgun, and you get into a deployment situation, it could snap his or her neck. Whatever, I don’t like f’ng around with the safety stuff, it should always be fixed properly is what I’m saying. And if you don’t want to spend the big bucks on a new part, get it out of a wreck at a yard, and fix it right, you guys should stop being a bunch of hacks, hate to purchase an E39 off of the likes of you.
    Set the controls for the heart of the sun

  16. #16
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    Sorry to bring up an old thread.
    I bought one of those ebay bypass dongle and it solved the airbag light.
    However, it doesn't show the seat is NOT occupied. So I thought it maybe the dongle is bad so I got 1N4007 diode and 4k7 resister wired up like op.
    No fault but still not showing seat is NOT occupied.
    Checked the resistance of my handy work and it's correct @ 4.75k Ohm.
    Thought I had a bad box and got 1 from local wrecker. Replaced box and still showing NOT occupied..?

    So I went for a higher resistor... 47k Ohm (10x) and still showing as NOT occupied.
    What is happening..?
    Last edited by wayneawh; 04-19-2021 at 10:36 PM.

  17. #17
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    Seat occupancy sensors

    I've see some problems with this thread. Because in the last 3 years I've looked up from my desk twice to see two head-on collisions on out 'quiet' neighbour road, in both cases both 201# cars were totalled with multiple airbags deployed, tyres ripped from rims and frame damage - sheesh it's a 20mph zone.
    Problems:
    OP (writing about e39) asserts "Passenger Seat DOT is white , which means system does not see any passenger, so airbag will work if an accident happens" ???????!!!!!!! Isn't that the opposite of what is meant to happen. I.E. Person detected and airbag goes off if - vehicle speed over X, if crash deceleration hard enough, if crash is on that side of car - this is so only the airbags needed are actually deployed.

    cpf9 suggests "When the sensor is working it DISARMS the passenger airbag when it detects no passenger, or a passenger under 40lbs (i.e. a little kid/baby, for whom the airbag could do more harm than good)." Indeed, but 40lbs ????? A kid could make 40lbs between 36 months and 78 months or 3 years (fat young-un) and 6.5 years (skinny whippet). Who wants an airbag going off on a 6.5 year old never mind a 3yo? But neither would be in a seat with out a child seat. The BMW ISOFIX base and baby seat probably weigh more than 40 pounds alone. While a 3.5 year plus seat weighs 15 pounds. Our 4yo weighs 35 pounds therefore 50 pounds altogether.

    Question-rhetorical at what age are children allowed to sit in the front? 12yo. Mean weight of a 12yo 90 pounds ~ 40Kg. BMWs are German. Germans work in metric (but German workers smoke in hazardous environments.)

    Still not sure about pyrotechnics in the face of a 12yo but better than hitting the dash. (German perception of risk again.)

    However, e39 is a design from the 1990s and I thought staged deployment started in mid-2000s. So in an e39 it's going off. Forgotten whether e39s had the 'key-in-the-hole-turn-off-the-airbag' switch - e65/66/67 didn't.


    A recently manufactured ECU can be different from an original. That alone can F up the car. It is safer to find a numbers matching part from a recycling yard and use that (VIN matching it with Auto-Hex if needs be), safer, more ecologically sound and half the M-Dlr cost.

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