Airbag light

    Yeah, that thought struck me too..


    BMW had the SRS2 system from 91-93 and the SRS3 is from 93-
    Since my car is built in '93 I realised there was probably a chance it had the SRS2 system. With SRS2 error no 2 is "Front sensor triggered - multiple times"
    The ignition circuit error message Carsoft gives me is on the SRS2 error code 44 and 45.


    To check this I ran a diagnostic check without the airbag connected, but I did not get any new errors.


    Source: http://www.scribd.com/doc/1703639/BMW-ERROR-CODES



    Of course I guess that there's the chance that Carsoft even got the error code wrong.
    Also when entering my VIN number into realoem.com the airbag module that came up is dated 9/93 - '96





    So I feel pretty comfident I got SRS3 installed, but I'm not 100% sure. I've asked a few places before, but no one could really confirm what system I have installed.


    No matter what I plan to go to the local BMW dealer and get a proper and full diagnostic of the car after this winter, but I was really hoping I could fix the few problems I know of on the car while it's in the garage.

    BMW diagnostics is probably the safest bet. Here is some blurb on the airbag systems used in the E31, however, I don't think either used the seat-occupancy detector:

    http://www.meeknet.co.uk/e31/BMW_E31_Airbag_System_ZAE1.pdf

    http://www.meeknet.co.uk/e31/BMW_E31_Airbag_System_ZAE2.pdf

    Okay, thanks for those links! I'll certainly read through them. Don't think I have a seat-occupancy detector either. As far as I know these are the correct schematics for my e31.

    My airbag light has just come on as well, this happened whilst driving and for no apparent reason, is it a big problem if I continue to drive the car with the light on whilst I get time to have a look at it? I am not a mechanic/expert so any simple fixes I could try would be helpful.

    No, it doesn't matter, but as long as the airbag light is lit the system is deactivated as far as I know. So in other words, don't crash ;)


    A reset with a reset or diagnostics equipment might clear the fault stored, if not you have to do a diagnose with the proper equipment.

    The seat occupancy mat is present in all cars with passenger airbags (only in passenger seat of course) and is also known to dislike being pressed in a non-bum fashion ;)


    Local deep indentations have led to the demise of said mats - unfortunately it is not exactly easy to replace.
    Replacing it comes close to a total dismantling of the seat. The leather hide is fastened with metal prongs and additionally stapled and glued to the seat frame. The seat occupancy mat and if installed also the seat heating mat are part of that makeup. If you do not know how to upholster a seat you will have to get it done.


    The ca. 4 Ohm resistor trick employed elsewhere might rid you of the light and help pass the MOT in case this is a MOT relevant failure.


    Cheers
    Reinhard

    Those resistors that Reinhard talks about can be bought as a "plug and play" connector off ebay for about 10$.


    I used one myself on my old E46 3-series and it worked like a charm! Took me 5 minutes top to install too.
    The only disatvantage, if you can call it that, is that the passenger airbag will depoly in an accident even if there's no one in the passenger seat...


    You will also have to clear the error stored in the airbag module after installing a resistor like that.

    This is starting to become a long thread, but I think I might just realised something here and hopefully this can help others with the same problem..
    I found another page with schematics to E31 built from 09/93 along with this information on another forum.

    Doesn't that leave the chance that the fault might as well be a short or broken circuit from the instrument cluster to the airbag control module? Does that sound reasonable?
    If so can anyone point me in the right direction on how to check this? I've never even removed the instrument cluster before..

    Thanks Reinhard and Trono, can I reset the light by disconnecting the batteries?, and if so, if it was just a temporary fault then the airbag light should stay off, am I correct in thinking this?

    I wonder if this is a similar problem to the one that affects the E32 750i. The EML light in the instrument cluster on the 750i consists of two bulbs just like the airbag light does on the E31 (if it is as shown in the circuit diagram). If one bulb fails, the EML system goes into failsafe mode. I believe that this is an anti-tamper system. Possibly this is the same system as used for the Airbag in the E31.

    I have seen a write-up on this Forum somewhere regarding the removal of the instrument cluster, it is pretty straight-forward, column fully out and down, same procedure for the E38, depending on the type of wheel you have it may need to be removed. Here is the procedure on the E38, I am changing bulbs here but these are not the bulbs for the EML/Airbag, see second link for those:

    http://www.meeknet.co.uk/e38/Instruments/Index.htm

    Here is a report of defective EML on an E32 and the position of the EML bulbs in the instrument cluster, in this case it is a PCB problem but I have seen the same problem when a single bulb fails:

    http://bmwe32.masscom.net/johan/eml_bulb/eml_bulb.html

    Aha, thanks Timm, that is some really interesting information! Heading out into the garage in a few minutes. If I figure anything out I'll let you know.


    Zitat von Deep;70969

    Thanks Reinhard and Trono, can I reset the light by disconnecting the batteries?, and if so, if it was just a temporary fault then the airbag light should stay off, am I correct in thinking this?


    No, the fault is stored in the module's memory and needs to be cleared with proper diagnostiscs equipment. You can buy this off ebay (i.e. Carsoft), but as mentioned earlier in this thread it is not the most stable system with such old cars. The best solution is to get it checked at a garage. Only problem is that they might charge as much as buying the carsoft cables from ebay.
    There are other reset tools too, but I have no experience with them.

    Both bulbs in the instrument cluster was fine. There was one removable and one soldered to the PCB. Just in case I also swapped the removable bulb with another one and checked continuity from pin 22 to 23 on the backside of the cluster.


    Also checked the wires from pin 7 on the srs control unit to pin 22 on the cluster. All is fine.


    Guess that leaves me the control unit again. :hmmmm:



    By the way, does anyone know if you can recode a used unit? As far as I know it's the same unit that's on the 7 (and 5?)-series. Atleast that would save me some money since I'm not even sure it'll work.

    It was worth a go! The 3-Series E36 had the same control unit as long as the build date is the same. E36:

    http://www.realoem.com/bmw/sho…&btnr=65_1096&hg=65&fg=65http://www.realoem.com/bmw/sho…&btnr=65_1096&hg=65&fg=65

    E31:

    http://www.realoem.com/bmw/sho…&btnr=65_1096&hg=65&fg=65


    The unit does not need to be coded if the donor car had the same equipment. The unit is coded for the inputs (occupancy sensors, seatbelt switches).

    Okay, that's good to know. I have access to a alot of E36 parts through friends. I'll see if I can find something suitable from there.


    Hopefully I'll have time to drop by BMW for a full diagnostics next week too.

    And the saga continues..


    I dropped by one of the local BMW garages today.
    They charged about £30 for a full diagnostics (another one in town wanted close to ~£200(!)) and when I got there they let me use their garage and equipment for a couple of hours trying to figure this one out. Good service! :)


    Anyway, the diagnostic gave the same error as I got with Carsoft, but with their equipment it also said Low Voltage as a detailed error. The samme error seemed to come again on several modules and the diagnostics eq got a communication error a couple of times. Many of the errors could probably relate back to when the old alternator stopped working, but communication errors can probably relate to low power.



    Since I first was there they let me test another control module and a third airbag just to eliminate those completly. Still the same error.


    Both my batteries should be fine and fully charged, so I guess I'm left with the extremly tiresome job of going over all connectors.



    I'm thinking about the option of connecting a smart charger in front under the hood and run another test, but not sure if that's very healthy for the electronics. Allthough I guess this older electronics can handle more than the very fine electronics in new cars. Anyone with any experience on this?

    Connecting a charger is a good idea, it is recommended by BMW for some diagnostic procedures (usually coding). It is a strange fault, although there is no chance of the airbag going off when probing the connections it would still scare me a bit. I would guess that good method of probing the drivers airbag would be to dismantle one of the modules and probe the connections from the inside. This should defeat the shorting link and ensure that the connector is sound....

    Low voltage messages normally stem from a time where batteries were disconnected.
    The best procedure to diagnose error messages is 1) read errors but don´t bother 2) delete errors 3) drive/wait 4) read again


    Else you will have to tackle tons of problems that may no longer be present.


    I doubt that with known good batteries you´d ever see a low voltage error message.


    BMW diagnostic equipment would normally also give an idea on how to master the challenge by way of a testing plan or a more direct method: replace this and that.


    Cheers
    Reinhard

    The low voltage message came back again instantly after deleting the error message. I had been out driving for 2-3 hours before going to the BMW garage as well as checking my batteries before to see that they both had a good charge. The mechanic told me that if I had one just slightly bad power connection and the airbag is usually the first unit that starts to fail in the car.
    We tried to clear all modules but the diagnostic unit crashed one time and got a communication error the next, so that's when he started suspecting a bad connection from the batteries.


    The diagnostic unit they had didn't give any more instructions on the airbag though, but just in case I ordered a new slip ring last night as that's pretty much the only "movable" part I haven't tried to change yet.

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