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Thread: Help diagnosing SRS airbag circuit fault

  1. #1
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    Help diagnosing SRS airbag circuit fault

    I have an "driver airbag circuit" fault in my '96 single-stage SRS.
    I measured resistance through the clock spring (aka slip ring) and found 1ohm for both red and white wires...but then I found 1ohm between red on one end and white on the other, and vice versa. So that means there's a short between those wires, yes?

    Resistance through the airbag itself was 0.4ohm. Is that correct?

  2. #2
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    Get proper diagnostics and read the fault codes
    No warranty of any kind implied or given and no liability for any loss, damage or injury, no matter how incurred accepted.

  3. #3
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    The fault is "driver's airbag firing circuit" as reported by my German specialist indy shop. Code 2 from the ZAE module.

    That fault can be attributed to a malfunctioning clock spring or to the airbag itself, which is why I started measuring resistance through the circuit. I'm not sure what you mean by "get proper diagnostics"--that's what I'm seeking help for here.

  4. #4
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    Well something like DIS not only reads the fault code but usually gives more info than generic codes and even has diagnostic procedures to help
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  5. #5
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    Ah ok. They told me what they got from the scan and said the most likely problem was wiring (including the clock spring), and they would start with that, but it could turn out to be the airbag itself. So I started my own testing with those options.
    They didn't know any more than that without further testing. I don't have an appointment until the week after next. In the meantime, if anyone has ideas about diagnosing this fault, I'd appreciate it!

  6. #6
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    It may be you can replace two cheap things like those and need to look no deeper
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  7. #7
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    Replacing the airbag isn't cheap. And anyway I'd like to properly diagnose the problem before replacing parts.

  8. #8
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    It amazes me what you lot pay for old beemers and parts over there.

    - - - Updated - - -

    Testing by substitution is a valid method
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  9. #9
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    Quote Originally Posted by E36328Coupe View Post
    It amazes me what you lot pay for old beemers and parts over there.

    - - - Updated - - -

    Testing by substitution is a valid method
    Are you suggesting he throw parts at it? Replacing an airbag and clock spring will easily be $1000

    - - - Updated - - -

    OP, sorry i no longer have an airbag or clock spring or I'd take measurements for you to compare against

  10. #10
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    what was the end result of your investigation OP? I have the same error. Thanks.

  11. #11
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    Quote Originally Posted by scooper View Post
    what was the end result of your investigation OP? I have the same error. Thanks.
    I had high resistance faults in first the passenger than driver's airbag firing (squib) circuits, and at one point actually measured a slightly too high resistance in the driver's side circuit. The airbags and clock spring all looked and measured good, so I suspected fretting corrosion and sprayed all the contact pairs from airbag controller to airbags with a precious metal contact lubricant (1-2% five-ring polyphenyl ether (PPE)). Here is a candidate if you are in the U.S. I have had no faults since.

    That very well may not be the problem, but might be something to try.

    PLEASE NOTE THAT measuring the resistances is a little tricky and you really don't want to generate any static electricity and inject it into a circuit. I wear a ground strap connected to the chassis when I have do such things.
    Last edited by johnf; 08-14-2018 at 10:14 AM.

  12. #12
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    Thanks John. I will try the PPE based spray first. I've had to do that before on the module under the rear bench seat. It worked.

  13. #13
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    Whenever working on the airbag system or even the seatbelts if they are the pyro variety you have to disconnect the battery negative and wait 10-20 min.

    Others have said that it is just corrosion on the contacts for the airbag system. Personally I fixed the seatbelt connection and fixed the fault code, most people replace the latch system at great cost.

    An alternative that is common here in the US for contact cleaner spray is Deoxit %5, the cost is kinda high $20, but they have a liquid syringe version that is only $6 on ebay. Be sure to read on how to use it properly before using.

    https://www.ebay.com/itm/DeoxIT-D-Series-D100L-Squeeze-Tube-100-solution-2-ml/361481715388




    - - - Updated - - -

    https://www.ebay.com/itm/Caig-Labs-D...p/401119171951
    Attn. NEWBIES: Use the search feature, 98% has already been discussed.
    Click the search button, select "search single content type", select the "e36 sub forum" specifically, try the "search titles" then try the "search entire posts".

  14. #14
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    Quote Originally Posted by Eric93se View Post
    Whenever working on the airbag system or even the seatbelts if they are the pyro variety you have to disconnect the battery negative and wait 10-20 min....
    A later E36 SRS only takes a few seconds to disarm.

    It is fairly hard to accidentally fire an airbag. One way is to unplug an airbag at the SRS controller, defeat the shorting shunt inside the plug, and inject some static electricity into the firing circuit while you are measuring its loop resistance. (A DMM, alone, is not enough).

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