Unable to get info from SRS module

    Hi.


    Yesterday, after some minor changes replacing a bulb at the instrument cluster, the Airbag light started flashing.. I tried to get the error code and/or erase the error message using the DIS... but no luck... as the SRS/airbag module refused to communicate with the DIS ( other modules worked.. ).


    I have checked all the wires coming to the airbag and everything seems to be ok, but SRS module still refusing to be reached by DIS...


    All fuses are ok, and looking at the ETM i am not able to get any clue about what can be happening...


    Any advise ?


    Thanks in advance.

    Hi.


    No luck, neither with disconnecting batteries. I have read somewhere that moving the key switch to "start" with the cluster disconnected can cause this error ( at least airbag light ) and that a special tool was needed. I supposed that GT1 will be able to do this... but still no luck. May be the module has gone bad ? How could it be checked ?
    I have checked airbag at the connector ( +/- 4 ohm ) with batteries disconnected and avoiding the microswitch at the connector to close the loop., so it does not look a physical airbag issue.


    Cheers,

    Zitat von dudu;102199

    I have read somewhere that moving the key switch to "start" with the cluster disconnected can cause this error ( at least airbag light ) and that a special tool was needed. I supposed that GT1 will be able to do this...

    The airbag warning light goes on as soon as a component fails when the ignition is on. The failure can be a disconnected airbag, bad seat occupancy map, bad contact,... Even after resolving the issue, the light will not go off unless the errors stored in the airbag module are cleared (disconnecting the batteries has no effect). Clearing the errors is easy through diagnostic software like BMW DIS or INPA, but your issue seems to be that the diagnostic software cannot communicate with the airbag module itself. This is a bit of a problem because you don't know what error is stored and you cannot clear it either. The fact that the diagnostic software cannot communicate with the module may hint at a bad airbag module. I'm afraid I know no other way to test it than to exchange it with another module.

    Zitat von revtor;102217

    The fact that the diagnostic software cannot communicate with the module may hint at a bad airbag module. I'm afraid I know no other way to test it than to exchange it with another module.


    I have just got a replacement module and will be testing along the weekend ( after disconnecting batteries.. )


    Quick question... Do you know if it will require from a recoding to match with the car´s VIN ? Car is a 1990 850 and SRS module a "6577 1382905" ( same ref as mine ) from an E34...


    Thanks.

    Zitat von dudu;102648

    Quick question... Do you know if it will require from a recoding to match with the car´s VIN ? Car is a 1990 850 and SRS module a "6577 1382905" ( same ref as mine ) from an E34...

    In the early cars the VIN is not stored in the airbag module, but the module will require recoding nevertheless because all crash parameters will be set to the E34. In DIS select "Coding/Program." > "[3] ZCS/FA CODING" > "[1] E31 Series" > "[1] Recoding" > "[19] AIRBAG" and follow the instruction. Make pictures of the new airbag module's labels. You might need some of the numbers later on.

    Zitat von revtor;102651

    In the early cars the VIN is not stored in the airbag module, but the module will require recoding nevertheless because all crash parameters will be set to the E34. In DIS select "Coding/Program." > "[3] ZCS/FA CODING" > "[1] E31 Series" > "[1] Recoding" > "[19] AIRBAG" and follow the instruction. Make pictures of the new airbag module's labels. You might need some of the numbers later on.


    Thanks revtor. Will update.

    No luck.


    Just replaced the SRS box with a replacement one, and same issue... Airbag light flashing at "I" key switch position , also at "II".


    Tried to recode new SRS box, and the car is not able to find it... I have tested replacing the N17 relay.. no luck.


    Will check if +12V present at the SRS plug when key at "I" or "II"..


    Thanls.

    It's unlikely the replacement airbag module has exactly the same failure and since diagnostics worked before (and still do on other modules) I don't think there's an issue with that either. Nevertheless, you may want to try INPA just to make sure.


    Anyway, this looks like a wiring issue in my opinion. Make sure the airbag module is properly grounded with the screw connection! Measure continuity between the metal enclosure of the module and a ground point somewhere in the car. If that's okay, check voltages and continuity at the X74 airbag connector. Depending on the month of production the connector is either 8-pin orange or 12-pin blue.


    8-pin orange

    • 1: 12 V as of ignition key position I
    • 6: RxD - measure continuity to pin 15 of the underhood diagnostic socket
    • 7: TxD - measure continuity to pin 20 of the underhood diagnostic socket


    12-pin blue

    • 12: 12 V as of ignition key position I
    • 6: RxD - measure continuity to pin 15 of the underhood diagnostic socket
    • 7: TxD - measure continuity to pin 20 of the underhood diagnostic socket

    With regards to the airbag light in the cluster... If you wait approximately one minute after turning the ignition key to position I, does the airbag light stop flashing and light up continuously? Or does it keep flashing forever?

    Zitat von wokke;104130

    I understand that there is a communication issue between DIS and the airbag module. I've had that before as well. So I used INPA and no issue whatsoever.

    It's my understanding that DIS used to work on the airbag module, so I doubt it's a software issue. Nevertheless, I would try INPA as well. You never know...

    Zitat

    I personally prefer INPA and only use DIS if I have no other choice.

    INPA is great for quick diagnostics and live monitoring, but for troubleshooting electrical problems nothing comes even close to DIS. The main issue of DIS is its horrible mouse performance when running in a virtual machine, but I found a very effective workaround for that. INPA is not without its communication issues either. Until quest hacked the DME files INPA could not be used on the M70 and there's still a data corruption issue between INPA and the E31 EKM module.

    Zitat von dudu;104138

    Regarding the airbag light, it lights up continuously after flashing for one minute.

    Well, basically that's good. This means there is (or was) a fault in the system but at least the airbag module is working. I don't think there's anything wrong with the power to the module. Otherwise that would not have worked... You still might want to check for continuity between the Rxd and TxD pins of the diagnostic plug and airbag connector, but I would recommend to try INPA first.


    In DIS, is there absolutely no communication with the airbag module? If you select "[19] AIRBAG" and click next, do you get a control unit not found error or do you still see the module's hardware & software versions, coding index,...? If you perform the "Short test" on the DIS E31 control unit survey screen (ignition key in position I or higher), is the "[19] AIRBAG" entry visible after the test completed?

    Zitat von revtor;104139

    In DIS, is there absolutely no communication with the airbag module? If you select "[19] AIRBAG" and click next, do you get a control unit not found error or do you still see the module's hardware & software versions, coding index,...? If you perform the "Short test" on the DIS E31 control unit survey screen (ignition key in position I or higher), is the "[19] AIRBAG" entry visible after the test completed?


    No airbag module ( 19 ) found at the short test. When tried to test the module running a specific tests it said that need another 30 seconds to reach it, and then, after some time a lot of messages telling that i should test power supply and connectivity for TX and RX lines, showing some resistance values.


    According your first paragraph, the module seems to be working, what looks promising. Will check INPA and also INPA at another old computer i have around ( the laptop is a DELL and i have read some post about old DELL serial ports no running fine with DIS... )

    Somebody has suggested to full load the batteries just before running more tests... Yeah, i know... rule number one on this car... :banghead: :banghead:


    Now recharging. Let´s do the CTEK XS7000 made its magic on the 8er....


    Will update as soon as they will be fully charged and a few tests have been done...


    Cheers.

    Well, batteries fully charged, tested with a laptop and also with the desktop computer using DIS... same behaviour... Then with INPA... "no module found".


    Time to do the hard work and start checking the wires revtor pointed.. Will update ( i hope this weekend.. )


    Thanks for your patience and support.

    Still trying to solve this...


    There is connectivity from the SRS module ( the 8 pin orange X74 ) to the diagnostic head ( 6 and 7 from SRS to 15 and 20 at the diagnostic head ) and seems to be 12V at the pin number 1....


    I have replaced the current module with the replacement one ( after disconnecting batteries ) and still not able to get info... When checked at the diagnostic plug.. and checking the pins suggested by DIS, it seems that pin 15 has low voltage...


    Any clues..?


    Thanks

    This is getting stranger and stranger... The module not getting power would obviously explain the inability to diagnose it, but if that is really the case I wonder why the airbag light stops flashing after one minute. It is my understanding the airbag module controls this behavior, so how is this possible without power?


    Just to confirm; if you disconnect X74 and turn on the ignition what does the airbag light do? The light should show no sign of life.


    The ignition switch is okay. Several items in the car get power directly or indirectly from the same ignition switch contact and you would certainly have noticed other issues if that was bad. There's of course still the possibility of a broken wire to the airbag module, but to be honest I believe the power to the module is okay - otherwise you would not have observed the flashing airbag light. Either you measured the voltage incorrectly, measured the wrong pin, or there's an error in the diagrams and power is not on pin 1 but another one...


    Can you confirm the wiring of X74 (towards the car) is as follows?

    • pin 1: violet
    • pin 2: black with green stripe
    • pin 3: - (no wire)
    • pin 4: blue with black stripe
    • pin 5: - (no wire)
    • pin 6: white with yellow stripe
    • pin 7: white with violet stripe
    • pin 8: - (no wire)

    Thanks Revtor.


    Yes, you are right.. i was not checking the pin correctly...Once done properly, i have measured the 12V at pin 1.. but still the same issue.
    I will run a short test as i remember that there were some message about a shortcut somewhere... may be this shortcut is causing some troubles to the SRS module.


    Cheers

    This is frustrating as everything seems to be ok and no error messages now at the car... Next step is ... connect the diagnostic head directly to the SRS module connector ( X74 ) bypassing the pins 6 and 7 ... that is


    • pin 1 at X74 (+12V ) to pin 14 of the diagnostic head
    • Ground to pin 19 of the diagnostic head


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


    For pins 6 and 7 i will disconnect cables ( with a switch ) from X74, but the question is... if connected directly ... will DIS/INPA work or will i need a specific reset tool like SIR3 ?


    Thanks.

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