BMW 320d e90/91 airbag fault 93B4 drivers airbag stage 2


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By wolf3199 - Monday, May 27, 2013 5:58:44 PM
Hi everyone

New to here and am here to try and get some clarity to my problem, I have a 2006 320d with the airbag fault 93B4 showing (LAUNCH DIAGUN) I have checked all wiring from the airbag ecu to the and including the clock spring each wire is giving an OHMS reading of around 1.4 , I also have fitted a donor airbag and still no luck Sad also have dissconnected and cleaned the plugs underneath the seats ,, has anyone came across this problem, car is one owner from new and never been damaged altho last year the light came on after the driver hit a rut on the road and a BMW dealer re set the light and she thinks she hit a pothole about a week later and never bothered about it until now as it is due an MOT

Any help is greatly appreciated
By RichTT - Monday, May 27, 2013 6:09:17 PM
So just to be clear, you have a fault for drivers airbag so you mess with wiring totally unrelated under the seat?

Which airbag have you donored and how have you checked clock spring?
By wolf3199 - Monday, May 27, 2013 6:29:52 PM
hi

I checked the plugs under the seat because if you google bmw airbag faults it refers to a lot of problems from bad connections under the seats so i just tried it w00t I checked across the clock spring for continuity and ohms is this correct? Oh and i donored the drivers airbag
By miketribe - Tuesday, May 28, 2013 2:34:24 AM
Wolf,

I checked across the clock spring for continuity and ohms is this correct?

each wire is giving an OHMS reading of around 1.4

I guess you have given yourself the answer then.

What do you think the resistance shoud be?

Mike
By wolf3199 - Tuesday, May 28, 2013 7:08:30 AM
Ok hold on I am testing the loom from the airbag ecu up to the drivers airbag with both units dissconnected!! Google was a nosey too see was the fault common with BMW!!

The resistance measurements were taken on the loom from the ecu up to the clock spring and then accross the clock spring this is where I am getting 1.4 ohm on each of the four wires from ecu to airbag , I know the 1st and 2nd stage igniters are in the airbag so the customer got a second hand airbag and i fitted it but same fault is there. What should the resistance readings be?
By xBenn - Tuesday, May 28, 2013 7:08:42 AM
When testing the clockspring you need to have it disconnected completely from the airbag circuit The small current from a multi-meter used to test ohms can set off the air bag.

All you are testing the clock spring for in the most basic sense is to make sure you have a connection from the input side of the clockspring to the output side going to the airbag. So you should be testing the clockspring on it's own as a single component. Basically, you want to check there is continuity across the clock spring.

1.4 OHMS is not right - i'm not quite sure how or where you measured to get that reading.. but IF you have tested it correctly and you are sure you are reading 1.4OHMS then the clock spring is faulty...

If you don't know how to test it, please leave alone - if you are still planning on testing it, make sure it is isolated from the airbag (as there is nothing dangerous within the clock spring it'self)

Also if you have a multi-function steering wheel fitted - that also passes through the clockspring
By xBenn - Tuesday, May 28, 2013 7:12:37 AM
You need to start by testing the clock spring on it's own!

Isolate the clock spring from the circuit and test from the input plug to the output plug on the clock spring - if you suspect the clock spring is faulty, testing from the ECU will not help you test the clock spring

- Also bare in mind, I am not suggesting the clock spring IS faulty, only how you can test it safely -
By wolf3199 - Tuesday, May 28, 2013 7:19:47 AM
Hi

I have tested the clockspring for continuity across all the 6 pins and all ok ( i know that the multifunction wheel eses this also) ill check my resistance across these again? I am also very aware of the dangers of airbags even though it does not read like that Smile can you explain what my resistance should be/
By K And R - Tuesday, May 28, 2013 8:35:14 AM
Wolf.

" I am also very aware of the dangers of airbags even though it does not read like that Smile can you explain what my resistance should be"

You are right it certainly does not read so, and asking about what the resistance across the clockspring should be, does not inspire any confidence.

I hope your customer is not paying for your learning curve.

Kev.

By xBenn - Tuesday, May 28, 2013 8:35:17 AM
Still assuming its the clock spring??

Think you need to start at the beginning... since although you say you are aware of the dangers im not so sure.

Have you checked live data to see what resistance the ECU is seeing on the STAGE 2 ignitor? don't know why you checked under-seat connectors. Do you know what a 2 stage air bag is?

Start by telling us what the data is telling you for the stage 2 ignitor?

If it's a fault with the airbag it'self, do you have resistors to be able to emulate the correct resistance of the airbag?


IF/When you've re-tested the clock spring post results on here - Also remember some clockspring faults are only present when the steering wheel is moved so test it with the clockspring reel in various positions?


Post this information and tell us what you think is incorrect/stands out..??
By wolf3199 - Tuesday, May 28, 2013 2:40:19 PM
Hi XBenn

Ok I am starting again from scratch ... obviously i should have little or no resistance in the the airbag loom or clockspring Wink I am getting continuity across the clockspring and a 0.3 ohm reading across the connectors, which seems normal.

The fault was in poor cables on the multimeter w00t which was giving him high readings yestersday ... I do not have a resistor or know the resistance to emulate the airbag or 2nd igniter in it ... although i have heard 3.3 ohms is correct but i aint goin near that one unless god himself gives me a go ahead..
The two stage airbag correct me if i am wrong (dont be a smart ass KEV we all have to learn BigGrin) is two explosions one after the other to inflate the bag? The reason i went for a donor bag was when i checked this car a few weeks ago and disconnected the airbag I had also a stage 1 igniter fault and with usually a component going faulty i opted for that route, I now am thinking the ecu could have a permanent fault internally as for live data i have not attempted that as yet as i am not near the car until tomorrow morning..Thanks for now
By K And R - Tuesday, May 28, 2013 3:30:10 PM
Wolf

"dont be a smart ass KEV we all have to learn BigGrin"

Yes we do have to learn, and there is a time and place for it and it isn,t on a customer,s car.

Lot,s of literature, course,s etc available if you want to learn.

Kev.
By RichTT - Tuesday, May 28, 2013 3:32:15 PM
wolf3199 (5/28/2013)
Hi XBenn

Ok I am starting again from scratch ... obviously i should have little or no resistance in the the airbag loom or clockspring Wink I am getting continuity across the clockspring and a 0.3 ohm reading across the connectors, which seems normal.

The fault was in poor cables on the multimeter w00t which was giving him high readings yestersday ... I do not have a resistor or know the resistance to emulate the airbag or 2nd igniter in it ... although i have heard 3.3 ohms is correct but i aint goin near that one unless god himself gives me a go ahead..
The two stage airbag correct me if i am wrong (dont be a smart ass KEV we all have to learn BigGrin) is two explosions one after the other to inflate the bag? The reason i went for a donor bag was when i checked this car a few weeks ago and disconnected the airbag I had also a stage 1 igniter fault and with usually a component going faulty i opted for that route, I now am thinking the ecu could have a permanent fault internally as for live data i have not attempted that as yet as i am not near the car until tomorrow morning..Thanks for now


Your testing still sounds lacking.

Continuity across the clock spring means to me it is shorted so can you elaborate on that test.

Checking for resistance wont help if the loom is hanging on by a strand.

Read live data for igniters and do as already said with resistors down the loom until fault goes.

If it doesn't by the time you are direct at ecu then you have either done it wrong or the ecu is kaput. Simple.
By wolf3199 - Tuesday, May 28, 2013 6:18:26 PM
I checked the clock spring inlet to outlet side for continuity all ok and no shorts to eaach other ... each individual pin gave .3 ohms across the clock spring ... thanks everyone for there help and comments
By xBenn - Tuesday, May 28, 2013 7:03:58 PM
This should really only have taken an hours worth of labour to button up

--
You should expect continuity from the input pins -> output pins on the clockspring (if that's what you did then that's correct) and resistance of around 0.3 would be acceptable through the clock spring. You will need also test while manipulating the clock-spring into different positions to make sure the fault is intermitent But like I said,
Still assuming its the clock spring??
it is unlikely that the fault is with the clock spring.
--

Did you read live data to see what ohms the ECU is seeing for 2nd stage ignitor?

Disconnect the second stage ignitor and substitute the airbag with the "correct" resistor - if the fault resets with the correct resistor then the fault lies with the airbag, if not then the fault lies with the loom from ECU to the clockspring or the clockspring to the airbag.

If you can't figure it out from the information given to you in this thread, then no offence I think you need to go on a course - especially since it's such a safety critical device. We aim to help or direct but not walk you through the entire process, again no offence.
By Navarone - Friday, May 31, 2013 1:58:40 AM
Does any body have any referances to digital multi meters and air bags. No intentions of raising the risk level with a meter, for which I see limited reason to use on SRS systems. - Live data, resistors possibly in combination with the correct diodes/capacitors.

I'm sure you are aware of shorting bars?

It makes me think of mobile phones and petrol pumps. When women are far more likely to start a fire at the pump, phone or no phone.
By SB126 - Friday, May 31, 2013 3:41:21 PM
I have been doing airbag systems for years and have never felt the need to measure the resistance of an


air bag.


Maybe this is because i have seen airbags fired, and then they demand respect.
By Navarone - Friday, May 31, 2013 6:50:51 PM
Prince (5/31/2013)
Nav, there are multimeters out there approved by manufacturers but in practice there is normally no need to use a DVM to test resistance across an airbag - there are other ways to do that ellimination) as mentioned above.


Absolutly. I was just curious weather there had been any actual docmented cases of it happening
By xBenn - Sunday, June 02, 2013 7:29:47 PM
Well I think the original poster seems to have ignored mine and others advice anyways so might as well give up on this one.
By wolf3199 - Tuesday, June 04, 2013 5:55:32 PM
Hi XBenn

The fault was an internal one in the ECU, i used a resistor 2.2 ohm and traced back the circuit from the airbag (disconnected) and no difference, went to my local breakers and picke up an ecu from an 07 car with drivers and passengers airbags out... fitted to my car after disconnecting earth on battery re connected cleared all fault codes with my launch and no warning light.. all good, soory for not getting back sooner.

thanks again for everyones help Wink
By jho145q - Thursday, June 13, 2013 6:51:38 AM
Hi

I had exactly the same problem. 93b4, and the same solution. Change the MRS unit. Thanks for telling how you solved it!!

//Robin
By xBenn - Saturday, June 15, 2013 6:30:46 PM
Only just spotted these, well done on fixing it - hopefully you could see how the correct testing allowed to you come to the correct outcome!

As far as MRS modules, Z4 springs to mind, early warranty recalls and even rain water contamination. Keeps me fed.