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      05-21-2018, 02:23 PM   #1
cae93
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Airbag Fault

Hi All,

New member and new M3 owner, loving the car but have an issue I'm hoping you can help with, there seems to be a whole lot of bad information on this topic out there, but very little actually helpful.

My problem is that having changed my paddle shifters, I have an airbag warning, I have BT Tools and it tells me the error condition is still present so I can't clear the code. It is the drivers airbag so I assumed I had not connected something properly, but all looks ok. I can't get the BT to read any resistances, on any of the airbags, not sure if this feature is just not supported on the "enthusiast" version.

Is it possible that I actually damaged the airbag or it's control module? I was pretty careful throughout, I think.
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      05-21-2018, 06:34 PM   #2
cae93
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Quick update, it seems that BT Tools does not support the control module for the airbags in the "actual values", it will only read/reset the faults. Does anyone know if there is a tool/software that can access this? Apparently my M3 has the "ACSM2" unit, not "MRS5" which is supported according to the support at Bavarian Technic.

Can anyone help, or am I sending this to a BMW dealer along with a blank check...
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      10-22-2018, 11:37 AM   #3
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So after months of messing around with this and getting a scary quote from the local BMW dealer for either my airbag module or my control module needing replacement I decided to investigate this thoroughly and found something that based on the massive number of posts & youtube videos could be quite interesting.

The fault in the end was very simple, and fixable but so many people seem to treat this (as I did) as an annoying warning light issue, when in fact the consequence is that the airbag is disabled by this fault.

I will start by saying that this fault happened after I removed the steering wheel airbag and would not apply to anyone who has this issue just driving along. My car was throwing 93B4 ZK12 airbag fault and after running multiple tools I was able to ascertain that the issue was "resistance too low".

Also, very sorry for no pictures, by the time I had realized they would be useful it was fully re-assembled. Anyway, here goes with the fault-finding:

Disconnect battery

Pulling the airbag out again and replacing it with 2 2.7ohm resistors, re-connect battery, cleared the fault with BT Tools, fault is now gone so the control unit is OK.

Now the scary bit, given all the hype about triggering the airbag, measuring the resistance of the airbag showed 2.7 ohms on both sides, so that also looks fine. The trigger point to me to fix this came from a non M3/BMW forum where it was discussing the shorting bar in the connector which is a safeguard to stop unintentional triggering and needs to be push away during measurement otherwise you just measure the short.

So then came the root cause for my issue. The connectors support this safety feature with some little projecting posts in the clip that locks the connector in place, and these were broken off on one of my connectors. Moving the clip between connectors moved the fault, so I was sure at this point. The posts on the broken connector were only partially missing, and you would never know by looking at one of them that it was broken unless you knew how the connector and locking clip were intended to work.

It doesn't seem possible to buy these clips/connectors, or even the small wiring harness (someone suggested that it is only sold with the steering wheel), some options seemed to exist on e-bay but none claimed compatibility with the E9x models so i needed to find an at-home fix that wouldn't be sketchy.

So I was able to fabricate 2 small strips of a plastic sheet, about the right thickness and about 2mm long and insert them in holes where the posts go, Then putting the connector into place and inserting the clip forced the strips down as if they were the original posts. It's all captive in the connector so no risk of them going anywhere.

Then it was simple to just (re-connect the battery), clear the fault memory (BT Tools again), click the airbag bag into the wheel and we are all done.

I would just reiterate the if you have this fault, your airbag connection is shorted out so even if the module tries to trigger it it cannot fire. It's no longer just an annoying warning message at this point, you have no airbag.
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      10-23-2018, 09:49 PM   #4
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Itís pretty common for people to break the shunt tabs on the inflator connectors. Itís what causes the codes for resistance faults. Good work figuring it out.
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      10-23-2018, 10:47 PM   #5
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have you check if your car was part of a recall? because mine had a airbag recall
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      10-24-2018, 12:50 AM   #6
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Quote:
Originally Posted by deansbimmer View Post
Itís pretty common for people to break the shunt tabs on the inflator connectors. Itís what causes the codes for resistance faults. Good work figuring it out.
Thanks, it surprised me that given the huge number of issues people talk about with airbag faults that this was not more widely known.

Also, it seems like the cable harness is available to buy directly from BMW (despite what was posted in several forum posts).
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      10-24-2018, 12:55 AM   #7
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^^^So after months of messing around with this and getting a scary quote from the local BMW dealer^^^

I decided that in the future, I wouldn't try and "Shadetree Mechanic" my $80,000 BMW M3 anymore as maybe the Bavarian engineers had it figured out from the start!
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      10-24-2018, 07:52 AM   #8
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Quote:
Originally Posted by cae93 View Post
Also, it seems like the cable harness is available to buy directly from BMW (despite what was posted in several forum posts).
You can buy just about every BMW connector by itself. Including the Airbag pigtail 32306777641. Plenty of wrong information online, just have to do enough research on your own if you're going to DIY on these cars.
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      10-24-2018, 07:15 PM   #9
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Quote:
Originally Posted by scrammer View Post
^^^So after months of messing around with this and getting a scary quote from the local BMW dealer^^^

I decided that in the future, I wouldn't try and "Shadetree Mechanic" my $80,000 BMW M3 anymore as maybe the Bavarian engineers had it figured out from the start!
I wasn't even sure what that meant, but having looked it up I couldn't be further from that if I tried, but paying over a grand to fix something that turned out to be a small plastic clip on a $26 cable.....
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      10-24-2018, 07:19 PM   #10
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Quote:
Originally Posted by deansbimmer View Post
You can buy just about every BMW connector by itself. Including the Airbag pigtail 32306777641. Plenty of wrong information online, just have to do enough research on your own if you're going to DIY on these cars.
Just FYI it seems that the part number above is no longer available from BMW, you can now buy this one instead 32306998946 at approximately 4 times the price. The old one is still available on e-bay.
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