C5 Mk1 Airbag Fault

[2cvandy]

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.

Forgive me if I get this wrong, I'm still learning about airbag systems (learning more than I wanted to know tbh, I've been driving my 2CV quite happily without the damn things for 25 years now!).
But are you refering to the side crash sensors in the B pillars ? I was planning on checking the wiring / connectors to those tomorrow, along with pulling out the glovebox to check the wiring to the passenger airbag.
But if they were the source of the fault, wouldn't the diagbox say so ?

[xantia_v6]

I am not familiar with the exact wiring architecture on this vehicle, but the nature of the reported fault code seems to indicate a lack of communications with the ECU, which could be due to a wiring fault, or a missing supply voltage. It is not clear whether you have the ability to do any wiring checks yourself?

[2cvandy]

I am not familiar with the exact wiring architecture on this vehicle, but the nature of the reported fault code seems to indicate a lack of communications with the ECU, which could be due to a wiring fault, or a missing supply voltage. It is not clear whether you have the ability to do any wiring checks yourself?

Hi,
I too suspect that the fault lies outside of the ecu.
As for checking the wiring ? I'm comfortable with checking the connectors, and bypassing or replacing them if required. The biggest problem tbh, is knowing where all the wiring and connectors for the airbag system are to be found.
I wouldn't be comfortable with doing any continuity checks on the wiring, I don't feel I know enough to not blow an airbag accidentally, which is why I asked our local garage to have a look. As well as doing general repairs, they are auto electricians and a Bosch service agent, and of course they're French so will no doubt have repaired many C5 s before
But, they diagnosed the ecu fault almost 3 weeks ago, and I'm still waiting for them to find a replacement. I told them I'd already replaced it, and that I can easily get them another, but it cuts no ice. They won't look elsewhere for a fault until they've replaced the ecu with one from their own suppliers and they're satisfied that's not the cure, and who knows? Maybe it will be ?
I'll admit it's frustrating, but a Spanish friend of mine once told me, "the French have no word that conveys the urgency of mañana", he's not wrong.
In the meantime, time is running out for the car. The MOT runs out in a month and if it's not fixed I'll have to replace it, I can always use my 2CV but the missus refuses point blank to drive it
It will be a sad day if it gets scrapped over this, I know it's 19 years old, but it's only had 3 owners, been garaged all it's life and still drives like new.

[wheeler]

Depending on trim level some UK spec mk1 C5's didnt even have an airbag warning light, if there was a fault a message just came up in the central display. It sounds like yours is the same as i've not seen any mention of a warning lamp? Can you not just cover the message display with tape for the MOT equivalent? You could do this in the UK to pass the MOT.
I know this doesn't fix the fault but it could keep it on the road at least??
If i remember right all the mk1 airbag ECUs are the same, you just configure it to the spec of the car.
Before condemning the airbag ECU i would confirm all power supplies & earths are there and also check the body VAN lines.
Is this the only electrical problem with the car?

[2cvandy]

Hi,
you are correct, no airbag light on my car, just the central display.
I love the idea of covering up the display, unfortunately the car has already failed, so the tester has already seen the fault.
The MOT is a little different here in France, when the car fails it is given a 2 month ticket to allow time for repairs. If I take it back now with the display covered I think we would have a problem, plus of course there's an audible warning "ping" every time the message shows.
Had I known it was now a fail, I would indeed have made a cover for the display unit before going for test, it's never been an issue before and I didn't know the rules had changed.
You say that when changing the ecu I need to " configure it to the spec of the car". But everything I've read so far says the airbag ecu is "plug and play". Would you care to elaborate for an electrical novice please ? How do I know what the spec of the car is ?

"Is this the only electrical problem with the car?"
Well, it's a Mk1 C5, so there have been odd little gremlins over the past 8 years, but all sorted as they appeared. So at the moment, yes, this is the only fault.

The garage have just rang to say they've located another ecu, and it's booked in for Thursday afternoon.
So, hopefully they can resolve the issue.

[wheeler]

They will for the most part be plug & play. The configuration is basically which airbags it has. Some vehicles may or may not have a knee airbag for example. Same with curtain airbags & side airbags. As long as the ECU is from a car with the same airbags as yours it should be plug straight in. Even if it it had a different config it would just come up with a specific fault about the missing airbag. It would not likely have the fault you have now. The configuration can easily be changed with diagbox or Lexia.

[wheeler]

Dont know how it works in France but could you not take it for a new MOT somewhere else or is it logged centrally? Also a warning beep should not be a fail. The beep could be for anything if there is no visible warning message/lamp.

[2cvandy]

Dont know how it works in France but could you not take it for a new MOT somewhere else or is it logged centrally? Also a warning beep should not be a fail. The beep could be for anything if there is no visible warning message/lamp.

MOT stations state licenced here, that's all they do.
MOTs not done at garages as in the UK, and yeah, it's all on a national database.

[2cvandy]

I got the car back from our local Citroen dealer yesterday.
Broken wire in the loom to the air bag ecu.
Section of loom replaced, that'll be 180 euros please.
Could certainly have been worse.

So, happy bunny last night. Ordered the two tyres it needs and booked it in for an MOT re-test.

Drove it 12 miles to town this morning and "ping" - message centre is reading "Braking Fault" - big red STOP on the dash.
I drove it home (gently). Brakes seem to be working normally, not sticking on either, I know the pads are okay coz I replaced em at the last service.
Checked the fluid level when home and that's fine.
Hmmmm ?
I suspect it's more electrical gremlins, quite possibly disturbed while fixing the ecu problem ?
But before driving it the 20 miles back to M. Citroen I decide to pull the wheels off so I can physically check for any actual problems.

Except, I need to raise the suspension to get my trolly jack under the car, and the buttons on the centre console don't work any more !
The message centre thinks the buttons work, that tells me the car is going up, but it isn't.
The suspension pump runs when I get into the car or close a door, so that's working too, it's just not talking to the console switch.

I've dumped it at the Citroen dealer and told them to ring me when the damn thing's fixed.
I think I might change my number,,,,,,,,,,,,

[Gibbo2286]

I'd be looking again at the comm 2000, the internal flat wiring (clock spring) is very delicate and a slight mal-adjustment when fitting can rip it apart.

[2cvandy]

Car's back again.
M. Citroen says the problem was an electrical connector for the brake light wiring, he said it had been "crushed".
Hmmm ?
It's under the carpet in the LH front footwell,,,,,,,,,
very near to the airbag wiring connectors,,,,,,,,,,,,,,
I wonder who might have been working in that area recently,,,,,,,,,,,,?

Any way, M. Citroen was very keen for me to understand that this was not their fault, and that maybe a passenger with big boots had been carried ?
Whatever,,,,,, car is fixed with no charge so I'm not going to argue.

Not sure why that would stop the height controls working ? But they're working now.

But I've been ferrying the missus back and forth from the Citroen dealer in the 2CV that I've been chugging around in reliably for the past 25 years,,,,,,,,,,,,,,,,,, there's a lot to be said for simplicity .
So why do I keep looking at the C6 as a possible replacement for the C5,,,,,,,,,,,,,,,,,,,?
Will I never learn ?

[GiveMeABreak]

There is only one Airbag ECU that manages the whole system James in a C5 and most other vehicles.

The other parts are the sensors that detect impacts and an accelerometer.

@2cvandy: That code is not recognised up as a valid fault code....