C5 Mk1 Airbag Fault

[2cvandy]

Hello lovely Citroen people
I know this subject has had a few airings, trust me, I've read all I can find, but not found an answer.

I have a 2002 C5 estate, 2,0HDI ( VIN VF7**************[VIN obfuscated, can be read by forum staff] ).
I bought the car 8 years ago, and in all that time the central message display has always shown "Airbag Fault" each time you start the car.
Previous owner (a friend) had spent 600 euro (I'm in France) with the local main dealer who took his money but failed to find the fault.
As it wasn't an MOT fail, and doesn't show an airbag light, I wasn't too concerned.

I did look it up on the forums at the time, found the advice about the connectors in the passenger footwell and soldered the wires together, which made no difference.
I also found a thread that said sometimes a broken connection under the comms unit is the problem, the comms unit was replaced by our local Bosch agent a few years ago and I asked them to check, but they said there was no problem there.
I've also had it hooked up to a Lexia, which said the airbag ecu was faulty, this was replaced, and made no difference.

The problem is, the MOT law here now sees the "Airbag Fault" message as a fail, so the car has just failed.
I've got it booked in at the aformentioned Bosch agent tomorrow, but given the above I'm not hopeful of them finding the fault.

So good people, any advice on where else to look ?
Or is there a work around where we can turn the damn messaging off ?

I don't much relish scrapping a perfectly good car for the lack of an MOT just because of some faulty sensor somewhere, this is no old banger, it's been maintained fastidiously (and expensively) to keep it reliable.
Any helpful suggestions gratefully recieved.

[wheeler]

What is the actual fault code you are getting?

[2cvandy]

Sorry, I don't have a code reader.
I did take it to a local indy garage a few years ago, and he said the fault code said the airbag ecu was at fault, no other codes.
When I turn on the ignition the message on the central display reads "Airbag Fault", then it goes out.
If any other message comes up, such as seat belt reminder, key reminder, automatic wipers activated, etc, it shows again.
It's booked in at the garage tomorrow, I'll ask them for the fault codes it shows if they can't fix it.

[2cvandy]

Okay,
managed to get it hooked up to diagbox today

" Permanent fault - airbag ecu fault - VAN internal "

Code ; P1F40

any clues ?
ta

[2cvandy]

Just in case anyone is still reading,,,,,,,,

I've spoken with Sam at AirbagTeam and he tells me that ;-
a) new airbag ecu not available for this model.
b) my ecu cannot be repaired.
c) they've had no success fitting 2nd hand airbag ecu to Citroen C5 models, he says it just doesn't work.
d) not withstanding c) my only hope is to keep fitting 2nd hand units till I find one my car likes !

To re-cap ;-
the connectors under the front carpet have been removed and the wires soldered.
the Comm 2000 unit was replaced a couple of years ago due to other issues, but didn't cure the "airbag fault" message.

Following Sam's advice, I've just fitted another 2nd hand airbag ecu, predictably with the same result as last time, diagbox still reads the same ;
" Permanent fault - airbag ecu fault - VAN internal "
Code ; P1F40

I have our local garage searching for a 2nd hand ecu at the moment, because their test says that's the problem they won't look any further until they've tried changing it themselves (it's a French thing !).

So before I buy every 2nd hand unit on fleabay in an effort to avoid scrapping an otherwise excellent motor, is it possible to re-code a 2nd hand ecu to my car ?
Can I persuade it to accept the transplant ?
If anyone has done this already I'd appreciate some guidance.

Or could the fault actually be elsewhere ?

[wheeler]

The airbag ECU on this car is not locked to one vehicle so a second hand one can be used no problem.

[Paul-R]

Indeed. Many years ago my Mk1 C5 had a blown side airbag in the passenger. I left it like that until the MOT rules on warning lights changed.

Fortunately I had donor car in the drive (to my wife's eternal joy) and fitted the airbag and ECU from it (I didn't even try just the airbag) and the warning light disappeared immediately.

Your problem will be obtaining an ECU that definitely hasn't been involved air bag deployment.

[2cvandy]

The airbag ECU on this car is not locked to one vehicle so a second hand one can be used no problem.

I'm liking your confidence, so assuming we don't have 3 airbag ecu with the same fault, any idea where else we should be looking for the problem?

[2cvandy]

Indeed. Many years ago my Mk1 C5 had a blown side airbag in the passenger. I left it like that until the MOT rules on warning lights changed.

Fortunately I had donor car in the drive (to my wife's eternal joy) and fitted the airbag and ECU from it (I didn't even try just the airbag) and the warning light disappeared immediately.

Your problem will be obtaining an ECU that definitely hasn't been involved air bag deployment.

Hmmm. I've bought 2 from breakers so far, both described as "tested and fully functioning". Though I have no idea how they could test them?
I gave the fault code to Sam at AirbagTeam and he says it's a fault in the ecu, not deployment. If the ecu needed resetting after deployment they can do that, but he says they cannot repair this fault.
Any advice for a reputable supplier who will have one " that definitely hasn't been involved air bag deployment"
I'm assuming that Citroen didn't make the ecu themselves, does nobody offer an aftermarket replacement new ?

[Hell Razor5543]

I would go visit your local scrap yards. If you find a C5 (of suitable spec and vintage) that has not had its' airbags deployed the ECUs could be useable.

[2cvandy]

I would go visit your local scrap yards. If you find a C5 (of suitable spec and vintage) that has not had its' airbags deployed the ECUs could be useable.

I'm in (very) rural France.
The only local breaker is 30 miles away, and the last time I went there he wanted 50 euro for a cracked windscreen washer bottle !
Our local "garagiste" has been trying to find an ecu for a couple of weeks so far, and he hasn't come up with one yet.
Part of the problem may be getting one of the same spec, my car is a RHD Exclusive, I don't even know if the French C5 was the same spec ?

[Paul-R]

I hate to suggest this but are you sure that all airbags and, especially, seat-belt pyrotechnic retractors are good? The seat belt retractors could have blown and you wouldn't really notice this.

I don't know what code reader your garage is using but it really needs a session with a Diagbox to check what's what.

[Hell Razor5543]

I would be very surprised if the ECUs were different. For every 'country specific' component there is on a vehicle there will be an increase in costs (and complexity as well, as there would need to be (for example) a German build, a French build, and so on). Airbag ECUs would almost certainly be 'universal' components across the C5 range.

[2cvandy]

I hate to suggest this but are you sure that all airbags and, especially, seat-belt pyrotechnic retractors are good? The seat belt retractors could have blown and you wouldn't really notice this.

I don't know what code reader your garage is using but it really needs a session with a Diagbox to check what's what.

Lets face it, I own a C5, I'm not sure of anything
I bought the car from a mate 8 years ago with the fault already showing.
He was only the 2nd owner and he said the fault message appeared without any obvious cause and I see no reason to doubt that tbh.
I tried fixing it by replacing the ecu back then, but the fault code was the same so I assumed the fault must be elsewhere.
The usual suspects, wires under the carpet, and Comm unit didn't fix it, so we kinda gave up looking.
I don't know what code reader the garage used, I have a diagbox which I'd not been able to use since my old laptop died. But I've just downloaded the new software to check this fault and that is where the
" Permanent fault - airbag ecu fault - VAN internal "
Code ; P1F40
comes from.
The garage just told me the airbag ecu is faulty, so I'm assuming they have the same message on whatever system they used.
If the seatbelt retractors had fired, wouldn't the diagbox say so ? Or is there some physical way to check them ?

[Hell Razor5543]

There are several ECUs around the car that 'manage' the airbags. There is the main ECU (typically in the centre of the vehicle; on a Xantia it is near the gear lever!), one per side (again, on a Xantia they are near the reels for the front safety belts), and others dotted around the car. Depending on which ECU first detect an impact will then determine which airbags to set off.

On my second Xantia I had an airbag light lit. Once I had her read with a proper code reader we found the left side airbag ECU had failed. Replacing it resolved the problem.