[PARANOlD]

Bought my car used and didn't have airbag warning issues at all. After about 6 months, cranks started to get slow and I started to see the airbag warning so I assumed it needed a new bat. Got a new bat, installed it, regstered it - no airbag warnings.

About 2 months later, started to get the airbag warnings again so I figured the battery was wrong or the voltage was off or something. Upon inspecting the battery and the positive terminal... I don't appear to have an airbag cable at all.

Obviously there is supposed to be a cable running into the positive terminal, and with that disconnected, you will see the airbag fault. Does anyone know where the cable enters the rear of the car so that I can try to trace back and find it? I did a rear shock replacement and I'm wondering if while the liner was pulled back, I lost the wire back in there somewhere.

Is it at all possible that the wire was never in there and the fault wasn't being thrown for some reason? Thanks for any information.

[ctuna]

Your picture is to small its not clear what you are trying
to point out.

electical e90 pdf
http://www.google.com/url?sa=t&rct=j...,d.cGU&cad=rja
http://www.google.com/url?sa=t&rct=j...85464276,d.cGU
http://www.google.com/url?sa=t&rct=j...85464276,d.cGU

[PARANOlD]

Picture with red box at top left shows the black wire connecting to the side of the positive terminal. That's the wire I can't find. Thanks for the PDFs. Sorry Google redirect-hosed you from your mobile device.

[gbalthrop]

Originally Posted by PARANOlD

Bought my car used and didn't have airbag warning issues at all. After about 6 months, cranks started to get slow and I started to see the airbag warning so I assumed it needed a new bat. Got a new bat, installed it, regstered it - no airbag warnings. About 2 months later, started to get the airbag warnings again...I don't appear to have an airbag cable at all.

What you are describing has NOTHING to do with airbags, BUT it IS part of the MRS (Multiple Restraint System). The part is called the BST or Battery Safety Terminal, and it is designed to "blow" the B+ connection on the part of the Battery Positive Cable that provides power to the Alternator & Starter in the Engine Compartment in the event the front collision sensors signal the MRS Module to send a signal to the BST pyrotechnic device.

Your "Cable" is there in plain view in your photo -- See the Blue & Brown wires on the forward side of the B+ terminal? Those two wires are attached to a connector at the BST, and that connector can become loose, and when it is NOT making proper connection to the BST, the MRS Module senses the open circuit & lights the "Airbag" (MRS FAULT) warning light. There is a specific code for the BST connection if you have INPA or BMW Scan Tool.

Here is the TIS circuit diagram showing the Blue and Brown wires going to the BST (G19a):
https://www.newtis.info/tisv2/a/en/e...rcuits/g6lHnMi

Perhaps someone who has had an issue with a loose connection there can describe how they fixed it (perhaps a small piece of Duct Tape ;-) -- whatever it takes to hold it in place. Removing the battery B+ cable, particularly if one does NOT know about the BST Connector, can/does damage the connection if NOT careful. Same for IBS on Negative Terminal.

EDIT: Upon Further Review of your post, you seem to believe the Blue and/or Brown wires (inside the black sheath) are disconnected at some point between the BST and the MRS(?) While that IS possible, I would suggest cleaning (with Electronic Contact Cleaner) the connector at the BST FIRST and fixing it tightly, with tape or whatever to see if warning light goes out, and STAYS out, BEFORE testing continuity of wiring between BST and MRS per the schematic above. BTW, you can click on the BLUE ID# for any component or connector and see Installation Location or Connector View, to make testing/tracing easier.

George

[PARANOlD]

Thanks for the info George. I should clarify that the photo example of the cable is not my battery, but of a battery with the cable present. The black wire that SHOULD be connected to the positive terminal is completely missing from the battery compartment area.

My issue is that I can't determine whether or not the wire existed before the car started throwing the airbag faults, but my guess is that it was connected and at some point blew out as you describe. It's very odd that the wire itself is not in plain view at all.

I will check other connections and attempt to hunt this black wire down from behind the lining area, I just don't immediately know the source location, so I will review the wiring diagrams first.

[dpaul]

You didn't say what error codes you've read, if you've read any. Since you keep referring to "airbags" I suspect you are just going by the warning from the iDrive screen.

You need to read the error codes - a common BST error in E9x cars is 93B2.
Maybe you actually do have an airbag fault or a fault in some other part of the MRS, rather than the BST.

That said, yes, there should be wires leading to the BST and if they are missing, then someone did something with them. I was experiencing a repeating 93B2 fault and didn't feel like spending $200 on a fancy battery cable so I cut the wires off and bridged them with a 2 ohm resistor to spoof the ASCM into thinking the BST was OK. Yes, someday I'll perish in a ball of flame because my electrical system didn't disconnect after an accident. In any case, I tucked the wires up under the trunk lining - they're no longer visible near the battery.

[Nickco43]

Originally Posted by dpaul

You didn't say what error codes you've read, if you've read any. Since you keep referring to "airbags" I suspect you are just going by the warning from the iDrive screen.

You need to read the error codes - a common BST error in E9x cars is 93B2.
Maybe you actually do have an airbag fault or a fault in some other part of the MRS, rather than the BST.

That said, yes, there should be wires leading to the BST and if they are missing, then someone did something with them. I was experiencing a repeating 93B2 fault and didn't feel like spending $200 on a fancy battery cable so I cut the wires off and bridged them with a 2 ohm resistor to spoof the ASCM into thinking the BST was OK. Yes, someday I'll perish in a ball of flame because my electrical system didn't disconnect after an accident. In any case, I tucked the wires up under the trunk lining - they're no longer visible near the battery.

Too much effort, just code BST out.

[dpaul]

Good idea - this was quite a few years ago and it didn't occur to me that it could be coded out. Would that be BPLUS_TRENNUNG1_1 or is it some other key?

In any case, that's an aside. The question is what happened to the OP's BST wires and whether he actually has a BST problem.

[smass]

Was your car in an accident prior to you owning it? If so the BST could have been coded out and if you did any coding, it could have been un-coded. "Code car" would do this. Or the bypass was done with a resistor which has come loose. Check all the battery wiring. BST wire runs across the top of the battery to the neg area where it joins the rest of the wires. The pic you posted is the newer BST, earlier cars have one that looks different. So post pics of your car just for sanity sake.

[PARANOlD]

Car was in a wreck at some point. Codes weren't thrown at all when I first purchased, only when the battery went low did they begin to show up. Now the airbag warning is back on the dash after battery replacement, but was cleared soon after installing the new battery, and then over time it came back. Could this be related to a Cobb tune, or is it more likely just a faulty manual hack? Here are the codes related to airbag:

93B0 - Head airbag, left
A66E - FZD

[dpaul]

Well, now you know the ABG error has nothing to do with the missing BST. So either the BST was coded out or the resistor fixed was installed. You can forget about that one for now. Also, the COBB tune cannot have anything to do with the issue you're having.

FZD is the module at the roof line above the rear view mirror. If I remember correctly it controls interior lighting, sunroof, microphone, SOS call button, LIN-bus gateway to the rain sensor and airbag indicator light.

So maybe that's the reason for the airbag light? Probably not. Any problems with any of the functions listed above?

Could be just a dirty connector - easy enough to locate, unplug, clean, replug

[dpaul]

Quick search for A66E came up with:

A66E:
Rear interior light error 0xA66E
Error will not cause a warning light
Test conditions have been completed
Signal or value below threshold "rear interior light"

So most likely, your major issue is a faulty driver side curtain airbag or a faulty connector.

[PARANOlD]

I started down the path of ripping open the overhead housing and checking the FZD, just haven't gotten to it yet. If I remember correctly, there are rear interior lighting issues after installing interior LEDs.

Sunroof works, haven't checked the rest of the functions.

I'm currently installing index 12 injectors and an upgraded LPFP, and will circle back to this problem once all of that is complete. Thanks for the info, I think we can assume at this point that there's a manual resistor hack in place and that the problem is related to the airbag connection itself or the FZD.