Unable to get info from SRS module

    Just connected the SIR3.. and flashing codes are for a "wiring issue" ( as you suggested ) .... so , will need to check all the wiring coming from /to the SRS module to check for some shortcut ( or open circuit ) "somewhere"....


    What i do not understand is that from the X74 connector there are no issues to the diagnostic connector at the hood...



    • pin 6 at X74 (RxD) - to pin 15 of the diagnostic head ( worked )
    • pin 7 at X74 (TxD) - to pin 20 of the diagnostic head. ( worked )


    so, what should i check and where ?


    Will update...

    You verified connection of the RxD & TxD wires between the underhood diagnostic socket and connector X74. Measuring 1:1 continuity between endpoints does not guarantee there is no short circuit in the wiring, but if there was a short circuit in these wires diagnostics of all modules in the car would be affected. Since you can still diagnose other modules in the car I think you can safely rule out the RxD & TxD wires. You also confirmed the airbag module gets power.


    Did you check the grounding of the airbag module? Measure resistance between the metal enclosure of the airbag module and another ground location in the car (preferably a reliable ground location like the ground nut on the left strut tower). The resistance should be a few ohms at most.


    Check connector X74's pins for corrosion and clean when in doubt - both on the car's end as the airbag module's end.


    If that is okay as well, I don't see what other condition can be missing for working diagnostics. It is possible there's a compatibility issue between the early airbag modules and diagnostic software like DIS and INPA (I don't know - I don't have much experience with early E31), but a simple reset tool like the SIR3 should work on all of them. Maybe one of the other wires to the airbag module is shorted and prevents the airbag module from working correctly.


    Unplug all connectors to the airbag module except for X74 and try again with DIS/INPA and the SIR3 reset tool. Note that with all these connectors unplugged there are plenty of permanent faults in the system so you will not be able to clear the fault codes. But that's not important at this point - before even thinking about clearing fault codes the communication to the airbag module should work. Is DIS/INPA now able to communicate? Does the SIR3 tool now no longer flash the red LED?

    Quick update....


    Connection to ground .- OK
    Red light flash for a few minutes ( not one minute as i said...may be 5.. ) , then stop flashing and keep light on...
    Disconnected all connectors... no lights ( obviously, no airbag... )
    Disconnected all connectors but the X74... same light behaviour... SIR3 same failure... DIS.. no module found...


    Will try tomorrow with cleaning the connectors and checking for some cabling issue at the X74 ( as the replacement module had the same behaviour )


    Will update.


    Thanks for your support and patience.

    more info...



    • pin 6 at X74 (RxD) - to pin 15 of the diagnostic head. Measured resistence below 0,5 ohms
    • pin 7 at X74 (TxD) - to pin 20 of the diagnostic head. Measured resistence below 0,5 ohms
    • SRS module screw to ground, below 0,5 ohms



    So, as revtor suggested, no apparent issues at Tx and Rx lines, neither at ground.

    I must admit that I'm not sure where to start from here. The diagnostic interface works and can reach other modules. The wiring to the airbag module is okay. The airbag module gets power and shows signs of life (the flashing airbag light is controlled by the module).


    I cannot find any reference to a 5 minutes flashing warning light in the electrical troubleshooting manual diagnostic procedures (ETMDP). It only mentions 60 seconds of flashing before going to solid when a fault is detected. On the other hand, the ETMDP covers only the 1990 model, so perhaps the behavior was changed in later airbag module revisions. I found an interesting thread at bimmerforums.com where someone experienced the 5 minutes flashing airbag light before going solid. In this case the issue was (probably) caused by a bad slip ring and fixed by replacing the steering wheel. This is not related to your issue, but it proves the 5 minutes flashing to indicate a fault is normal behavior for at least certain airbag module revisions. In other words, the 5 minutes flashing airbag light proves that your airbag module is actually working... It is of course possible the module detects an internal error (which may completely break functionality and diagnostics) and reports this through the flashing airbag light.


    I reread the thread and perhaps I misread it in the past... I always assumed the airbag diagnostics worked until you replaced the instrument cluster bulb, but is that actually true? Were you able to diagnose/clear the airbag module before this issue occurred? Did you successfully use DIS/INPA on the airbag module before?


    Which diagnostic interface do you use? GT1 yellow head? ADS? Something else?

    Hi dudu, I just read that you are still working on this problem and that even my SIR3 did not solve the problem so far. I am not sure if that helps, but read here post # 8
    info on SRS fault codes system 3, explanation >troubleshooting
    http://www.bimmernut.com/forum…light-reset-tool-new.html
    also post #9:
    about SRS light stays on 2-5 minutes:


    If you look at service bulletin 720496 you'll see it. It's caused by a broken or damaged circuit board in either the drivers side seat belt latch or the passengers side. If you have code 24 its the drivers side if you have fault code 25 its the passenger side, either way it goes into the default mode which is to trigger both bags in the event of an accident.
    IF the system is functioning normally then the seat belt sensors detect if you have a passenger in the car and will turn that bag on or off which would save some money if nobodies on that side then you don't need to trigger the passenger bag.


    It affects all models with the ZAE airbag system, E34, E36, E38, E31 as of production date 3/94
    ---------------------
    SIR3 error messages


    1. Red LED flashes before any buttons are pressed: >>there is a fault in either the SIR3 or the vehicle's wiring.


    2. Red LED flashes after an attempted resetting procedure:>>there is a communication problem with the system

    Zitat von revtor;107605


    I reread the thread and perhaps I misread it in the past... I always assumed the airbag diagnostics worked until you replaced the instrument cluster bulb, but is that actually true? Were you able to diagnose/clear the airbag module before this issue occurred? Did you successfully use DIS/INPA on the airbag module before?


    Which diagnostic interface do you use? GT1 yellow head? ADS? Something else?


    Hi revtor.


    Yes, i was able to diagnose the Airbag module in the past using the same hardware i am now using, that is, a laptop with a vmware running DIS and an ADS interface from rv8flyboy.


    Yesterday night i ran an exhaustive test on alll the modules trying to figure out if some other module could cause some strange behaviour, but no significative error messages... Also tried to connect ( once again ) the replacement module ( same reference than the one i currently have ), and the behaviour was the same when connecting the X74 plug ( no other plugs were connected at that time ).
    I will continue with checks along this weekend, but not sure how to proceed. Will try disconnecting the cluster and check if the airbag module is now able to "chat" with DIS due to something at the cluster causing this weird behaviour from both airbag modules ( the original one, and the one from the E34 ( still not being able to code it.. ))


    Thanks a lot.


    Thanks Shogun. i am now reading it, and have seen it suggest some other additional checks to do. Will provide measures on my car.


    Also, to clarify, the error i am getting from the SIR3 is the second one... communication error with the module. Next step is start checking the SRS module connecting the module side X74 plug to the SIR3.. This way, no external modules will be interfering it... Crossing fingers..


    Edu.

    I'm glad you finally managed to reset the airbag light :top:, but this whole issue is quite strange... Even though you measured the wiring to the diagnostic socket to be okay, it seems *something* is interfering with it. I'm clueless as to why this would only affect communication to the airbag module. All modules with diagnostics are connected directly or indirectly to the very same pins of the diagnostic socket and you had no issues reading those...

    Zitat von revtor;108509

    I'm glad you finally managed to reset the airbag light :top:, but this whole issue is quite strange... Even though you measured the wiring to the diagnostic socket to be okay, it seems *something* is interfering with it. I'm clueless as to why this would only affect communication to the airbag module. All modules with diagnostics are connected directly or indirectly to the very same pins of the diagnostic socket and you had no issues reading those...


    Yep, quite strange... I will try to check if i am now able to reach the SRS module from DIS... If it is working now, then "something" around got "confused" when the SRS went crazy.
    Also, in the past, i disconnect the whole cabling from the SRS module and was able to diagnose every module at the car ( well. not all of them , as i have not been able to diagnose the EGS since the beginning despite i have tested with several ads32.dll libraries .. but this can be a topic for another thread .. :grin2: ).


    Cheers.

    Bump... the strange issue with the SRS not able to communicate with DIS, seems to be causing some troubles to some other modules as revtor pointed... Now i am not able to get data from the EML/DME... ( neither from SRS... )


    How should proceed ? Disconnecting the modules one by one and check cabling can be a nightmare... but i have no other idea about how to deal with this..


    Thanks.

    Hi dudu,


    now I'm having the same issue on my black 1991 850i. Neither DIS nor INPA are talking to the airbag module. I changed my steering wheel and didn't disconnect the battery prior to taking the old one out. Stupid mistake but now it's too late. Did you ever manage DIS or INPA to talk to the airbag module? It does work on a 1193 model but not on mine.

    Zitat von wokke;119996

    Hi dudu,


    now I'm having the same issue on my black 1991 850i. Neither DIS nor INPA are talking to the airbag module. I changed my steering wheel and didn't disconnect the battery prior to taking the old one out. Stupid mistake but now it's too late. Did you ever manage DIS or INPA to talk to the airbag module? It does work on a 1193 model but not on mine.


    Hi Wokke. Nope, i have not been able to talk with the airbag module since i had the issue. As i was able to reset it using the E30 procedure and it worked, now i am in mode "if it is working, do not touch it.." ( despite it should work better... :grin2: ).


    Cheers.


    Edu.

    Zitat von dudu;120478

    Hi Wokke. Nope, i have not been able to talk with the airbag module since i had the issue. As i was able to reset it using the E30 procedure and it worked, now i am in mode "if it is working, do not touch it.." ( despite it should work better... :grin2: ).


    Cheers.


    Edu.


    Since this is a general issue with older E31-850i I got myself a special tool from Shogun which allows me to reset the SI (Oil service / inspection / yearly inspection / airbag).
    Price was €70,- and it works perfectly. I highly recommend it also for the DIY toolbox.

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