Technical Another Airbag, Seatbelt, Start-Stop thread

[sicarumba]

Hello all

Apologies for another thread which seems to have been covered a few times. I am someone who likes to do my own research and only ask questions when I can't find the answer (or get frustrated going round in circles) - and this is one of those times.

Wife's 2013 Fiat 500 1.2 Colour Therapy. She drove the car to work yesterday which is about 13 miles, and just as she arrived the dash lit up with the Airbag, seat belt and stop/start lamps. When turning the ignition on there are the usual messages about stop/start and fuel cut-off, and the odometer is flashing. From my research these are all symptoms of a loss of communication to the Airbag ECU.

After trawling through this forum I believe I have covered all the usual suspects. I disconnected the battery last night and left it disconnected overnight. The car appears to have the original battery so we bought a new one this morning, ensuring it was a beefy stop/start one, and at the same time renewed the two earth straps and cleaned all the contacts. Checked the Airbag ECU under the heater box and all the contacts look OK. Also checked the hatch wiring which all appears to be as good as new, no marks or cuts, nothing. Certainly looking like the Airbag ECU is at fault. However, some questions remain :

1. I thought about trying the MES software to try and get more information, I have downloaded the free one but do not have a suitable cable. I have found some differing information regarding which cable I should get (or I'm misinterpreting the information, either way some clarification would be appreciated) - some sources suggest I only need an ELM327 cable to talk to the OBD2 port and this will communicate with all modules, including the Airbag one, and I will be able to determine if the module is at fault. Some other threads I've read suggest I need different coloured adapters to talk to the Airbag ECU. Can anyone clear that up please, or ideally recommend the cable(s) I need? To me this sounds like the ELM327 cable will talk to the Body ECU which in turn talks to all the other modules, and will tell me the Airbag one is not responding, but won't tell me why. Getting the adapters will allow me to connect to the Airbag ECU and see if it's alive. Is that correct?

2. If the Airbag ECU is at fault and I get it reconditioned, will I still need the MES software to perform the Proxy alignment or will it just plug in and clear down the faults?

3. If MES is required, will the free one suffice?

4. Are there any other possible causes which I could go and check without any of the software/OBD2 cables?

Thank you in advance for any advice, I'm pretty tech-savvy so I'm happy to learn about these things. I don't want to buy the wrong thing and damage the car, or waste money when a quick forum discussion will clarify things.

 

[Baglady1990]

typecastboy this sounds like your specialty

 

[jrkitching]

Hello and welcome.

Your story is pretty much a carbon copy of this thread.

First thing to do in cases like this is to check the integrity of the hatch wiring; see here.

This is the sort of thing you're looking for.

 

[typecastboy]

It varies if you get it repaired whether it will need a proxy alignment, sometimes you do, sometimes you don't. In theory, you shouldn't as it's the same one out of the car. If you do, then MES will do it.

The free version of MES is as good as useless. You can do little or nothing with it.

You need the yellow adapter to connect to the Airbag ECU and most others.


First thing to try, believe it or not is the brake switch. £10 for one on Ebay , or thereabouts. Often the cause of what is believed to be ECU faults. For the money, it's worth trying first.

Certainly invest the 50 euros and a set of cables though, it'll pay for itself the first time you use it.

It could also be the clock spring and/or speedo but they are more unlikely.

Get MES and cables, plug it in, see what you get. You will probably get a failure error reading the ECU but that is your starting point.

I have replaced loads of these airbag ECU's. Try and get the same model number if you can. It's held in by 3 10mm bolts, two are easy to get to from the passenger side but the other one is the driver's side, at the back right hand side. Once you've disconnected the battery earth terminal, remove the two plugs, and pull them out of the way. You can then by feel, get a spanner or better still a small socket set in there and get the final bolt undone.


Good luck, and let us know how you get on.

 

[sicarumba]

Thanks all for the responses so far.

First thing to do in cases like this is to check the integrity of the hatch wiring; see here.

Yes, hatch wiring is one of the things in my initial post which I checked, funnily enough Maybelline was one of my search terms after a bit of reading. Having seen your picture I was amazed at how clean our wiring looks, it's as good as new.

First thing to try, believe it or not is the brake switch. £10 for one on Ebay , or thereabouts. Often the cause of what is believed to be ECU faults. For the money, it's worth trying first.

Interesting, thank you. I've ordered one, as you say for the money it's got to be worth a try.

You need the yellow adapter to connect to the Airbag ECU and most others..

Just to be clear, as I don't want to get it wrong, would you therefore suggest the bundle called "FESCAN" on the gendan.co.uk site? Apologies I'm not able to link the URL until I hit 5 posts, but at gendan.co.uk it's the only result for "FESCAN". If so it seems like a worthwhile purchase for the long term even if I end up needing a module and not needing to Proxy align - if the £10 brake light switch doesn't fix it that is!

 

[Baglady1990]

Thanks all for the responses so far.



Yes, hatch wiring is one of the things in my initial post which I checked, funnily enough Maybelline was one of my search terms after a bit of reading. Having seen your picture I was amazed at how clean our wiring looks, it's as good as new.




Interesting, thank you. I've ordered one, as you say for the money it's got to be worth a try.



Just to be clear, as I don't want to get it wrong, would you therefore suggest the bundle called "FESCAN" on the gendan.co.uk site? Apologies I'm not able to link the URL until I hit 5 posts, but at gendan.co.uk it's the only result for "FESCAN". If so it seems like a worthwhile purchase for the long term even if I end up needing a module and not needing to Proxy align - if the £10 brake light switch doesn't fix it that is!

Download the registered version from here https://www.multiecuscan.net/ then order a set of cables

 

[typecastboy]

Gendan site is a bit expensive. Buy the software licence for 50 euros direct on the MES website and just get yourself a basic ELM set up like this one.

https://www.ebay.co.uk/itm/162564786834?hash=item25d99dca92:g:3ycAAOSwT5xZTo2y

 

[sicarumba]

Gendan site is a bit expensive. Buy the software licence for 50 euros direct on the MES website and just get yourself a basic ELM set up like this one.

Spectacular thank you, exactly the information an OBDNoob like me needed. I've ordered the cables you kindly linked and I'll report back with my findings when I get everything talking.

 

[typecastboy]

On a Windows 10 laptop it should set up seamlessly. You may need to configure the Com port, but if you have trouble, ask on here. Yellow adapter is used for most ECUs except, from memory, Steering and Engine where you use no adapter, just the ELM interface.

 

[sicarumba]

Morning all

Brake light switch and OBD cables arrived today. Brake light switch has been fitted and has not fixed the issue.

Connected the OBD cables and launched MES. Attached to this post are the screenshots, they seem to be fairly consistent with the other threads I've seen on here but if I'm reading it right the ECU is complaining of communication with the Body Computer, but then goes on to list errors on the Body Computer anyway?

The Connection Failed shot is from when I attempted to connect to the Airbag module with the yellow adapter cable attached. Anything else I can try?

ETA - added 4th picture showing the Proxy alignment screen (I didn't try it, but I read about seeing module status in there) - sure enough, Airbag Node is Removed but the Body Computer is alive and well.

 

[sicarumba]

Quick update.

The guy in Kent who fixes these airbag modules and is mentioned on this forum a few times does a £20 test service, so I've packaged up the module and sent it to him to bench test it for me. I figured all the signs point to the module being the culprit and this way I'll know for sure either way. If it's duff I'll pay him to repair it, and if it passes I'll know the trouble lies elsewhere so I consider that a win/win for £20.

 

[sicarumba]

Hi all

Received the airbag module back from the repair guy today. Installed and turned on the ignition, stop/start light is gone and no messages about fuel cutoff, but a beep and "airbag failure message" happens and both the airbag lights are still on.

Connected MES, Proxi alignment option tells me all modules are fine and the procedure is not needed. Connecting to the airbag module and scanning for codes gives me this screen :



B0103-11 and B0104-11. Anything I can try before I start removing trim and carpet looking for dodgy wiring? Is it possible these alarms are from the test procedure and they will clear down on their own? EDIT - I tried to clear them and they came back, so not likely.

 

[sicarumba]

Me again

Having another play with MES and I managed to find the Parameters page of the airbag module, which shows the 1st stage resistance values to be very close to everything else. Does this look correct/incorrect to anyone?

 

[sicarumba]

OK this'll be my last attempt at this problem before I just take it to Fiat, because I'm getting nowhere and it's a bit beyond my understanding.

Contacted the airbag module guy who offered to check the unit again for error codes, he's reported back today to tell me it's all looking fine and the problem must lie in the car somewhere - it did have burnt out components and his repair was necessary, and that is reflected in the Proxi alignment page of MES so I believe him.

I've removed the driver airbag and tested the resistance of each stage, both read around the 2ohm mark which seems fine. My simple thought process was that the orange connector on the back of the airbag has 2 pins, therefore there must be 2 pins on the airbag module which correspond, so using a meter on continuity I should be able to find which 2. The trouble is each pin on the orange connector at the airbag end corresponds with 2 pins on the ecu connector, the same 2 in fact. The same story with the purple connector, so that would be both stages. Which makes me wonder, why does the parameters page of MES show normal readings for airbag resistance?

Anyone got any suggestions before I bite the bullet and lube up for a Fiat dealer invoice?

 

[Gina500]

You might feed the driver airbag stage 2 connector with a 2Ohm resistor and see if that makes a difference.
1 Ohm resistance is easily generated in bad connections or when the contact pressure is too low (e.g. a broken spring in the contact)

 

[sicarumba]

You might feed the driver airbag stage 2 connector with a 2Ohm resistor and see if that makes a difference.
1 Ohm resistance is easily generated in bad connections or when the contact pressure is too low (e.g. a broken spring in the contact)

I tried this today, not sure what to make of the results. Attached is a photo of my new patented airbag simulation tool, delivering about 3.5ohm each side. I removed the drivers airbag and connected both 1st and 2nd stage connectors to the tool and checked the resistance readouts on MES. 1st stage stayed at 2ohm and 2nd stage showed 3.5ohm. The same was true if I swapped 1st and 2nd stage connectors over. The strange thing is when disconnected, both stages showed 7ohm. So the 1st stage is reacting to being disconnected and is showing the same reading as the 2nd stage, but is shorting out as soon as it is connected to any form of resistance. Does that mean anything to anyone?

 

[Gina500]

Hm - I would interpret this as the sensing being faulty when it shows 2 Ohms while connected to 3,5. If I understand you correctly, the 2nd stage shows 3.5 Ohms in both cases (which would be correct but also close to what it showed with the real airbag.)
If the 1st stage shows 2 Ohms - which it did with the real bag as well - it may have a sensing problem.

Can you add a few resistors and make it 2.5 Ohms on one side and then measure one way and swapped ?

When you say 7 Ohms while disconnected, that means all 4 wires open ? Not sure what the computer is supposed to show in an open circuit. Maybe that´s the max programmed value ??

Or there could also be an internal resistance of the measuring circuit of 7 Ohms that then shows the resistance of the parallel circuit (7 and 3 Ohms parallel makes approx. 2 Ohms. In that case the 2 Ohms would be the correct readout value, not the 3.5)). Unfortunately I could not find any details on how these things look like internally.

In any case make sure the connectors are low resistance so they don´t generate a faulty reading


And it is highly recommended not to measure the airbag resistance directly !


As you have the simulator set up, you might vary the resistance values and see which port registers any changes and which one doesn´t.

My overall suspicion would be that the airbag control module has an issue, though.

 

[sicarumba]

Hm - I would interpret this as the sensing being faulty when it shows 2 Ohms while connected to 3,5. If I understand you correctly, the 2nd stage shows 3.5 Ohms in both cases (which would be correct but also close to what it showed with the real airbag.)
If the 1st stage shows 2 Ohms - which it did with the real bag as well - it may have a sensing problem.

Yes correct, 1st stage shows 2ohms when connected to anything and the "short to ground" fault is present.

Can you add a few resistors and make it 2.5 Ohms on one side and then measure one way and swapped ?

I brought it all the way down to 2.1ohms using lots of resistors (I only have 10ohm ones). Connected to the 2nd stage and that showed 2.5ohms. Connected it to the 1st stage and it showed 2ohms again. I also tried a single 10ohm resistor in each. The 2nd stage remains at 7ohms, the 1st stage goes to 2ohms. I did wonder if the MES software only goes down to 2ohms?

When you say 7 Ohms while disconnected, that means all 4 wires open ? Not sure what the computer is supposed to show in an open circuit. Maybe that´s the max programmed value ??


Or there could also be an internal resistance of the measuring circuit of 7 Ohms that then shows the resistance of the parallel circuit (7 and 3 Ohms parallel makes approx. 2 Ohms. In that case the 2 Ohms would be the correct readout value, not the 3.5)). Unfortunately I could not find any details on how these things look like internally.

Yes, with all 4 open. If I disconnect either stage, that stage goes to 7ohms. I was assuming the same, that either it is some form of resistance in the overall circuit or the software maxes out at 7. With both stages disconnected and checking the fault codes on the module the "Short to ground" is replaced with a different code, meaning it is aware of the circuit being open and no longer shorted.

And it is highly recommended not to measure the airbag resistance directly !

Too late, already checked it last week. Measured around 2ohms so won't be doing it again.

My overall suspicion would be that the airbag control module has an issue, though.

I hope not, the guy who reconditioned it seemed confident it passed his tests and he's already had it twice, I'd hate to have to send it to him a third time and ask for my money back!

 

[Gina500]

Ok, no further ideas on the airbag end of the connector. So maybe the wiring or connectors are at fault. Maybe the spiral connector at the wheel has an issue ?
Can you do the same measurements but connecting the resistors to the module end with your own wires? If that works then it's probably the wires. Difficult, though, you would need to bridge all the other wires for power, bus etc. to getvthe nodule working at all. Hm.
I will send you some pages from the training book that I found. That may help test the wiring individually.

 

[sicarumba]

Ok, no further ideas on the airbag end of the connector. So maybe the wiring or connectors are at fault. Maybe the spiral connector at the wheel has an issue ?
Can you do the same measurements but connecting the resistors to the module end with your own wires? If that works then it's probably the wires. Difficult, though, you would need to bridge all the other wires for power, bus etc. to getvthe nodule working at all. Hm.
I will send you some pages from the training book that I found. That may help test the wiring individually.

Thank you very much for the training info. The pinout was exactly what I needed to further pinpoint the issue. Apologies in advance for the multiple images.

Firstly, I connected the power/canbus and driver/passenger 1st stage airbags up directly to the connector but via my external wires, just to prove the error is still there. I didn't have enough cables to wire 2nd stages at the same time, nor the knee guard / ECS, but hopefully this will still be relevant to pinpoint the problem.

Wired up like this :


Errors are as expected, 1st stage still shorted. 2nd stage and knee guard are open circuit :


And parameters :


Next I wired the driver and passenger 1st stage pins up to my dummy resistance, which is about 3.5 ohms.

EDIT : like this :


But, the errors are still there :


And parameters :


Just to prove it wasn't an old error (I am clearing them each time BTW) I disconnected the dummy resistances and the faults changed to open circuit ones :


Forgot to capture the parameters page here, doh!

Connected dummy resistance to drivers side only, 1st and 2nd stage. The 2nd stage error is gone meaning my dummy resistance has been accepted as an airbag :


And parameters :


Did the same on the passenger side 1st and 2nd stage, again no 2nd stage error for the resistance connection :


And parameters :


As the wiring harness has been eliminated from the circuit and I am connected directly (via some short cables) from the module to a known good resistance and I am still seeing the short circuit problems, doesn't this suggest the airbag module is the culprit? I'm leaning towards buying one from eBay and finding out ....