Airbag light: Part no for Xantia for steering column slip ring

[RichardW]

You don't really need a resistor, just unplug the air bag(s) and the pre-tensioners, and then you can check continuity from the plug at the ECU to the various end 'users'. You might also want to check that you have power at the ECU - it might operate in the same way as the ABS in that the light is separately powered, so that the light comes on if the power supply is lost.

[vmaxvmax]

Great, thank you all for your help on this frustrating journey...

I'll get to it over the weekend and update this thread with progress.

I may still need to fool the replacement ECU into thinking that there is a passenger airbag if the replacement is so configured in the event that everything else seems good. My Citroen dealer wants an arm and a leg per visit.

In that case I presume a 2.2 ohm resistor across terminals/pins 9 and 10?

Merci beaucoup...

[RichardW]

Hopefully Chris (white exec) can post up the relevant wiring diagrams so you can see what pins are what. It looks like there are 2 spare sets - I imagine one is for the passenger air bag (which will need a resistor) and the other is for the passenger air bag disable switch (which will need a direct bridge).

[vmaxvmax]

Hadn't though of that! Thank you!

Most of the phase 1 Xantias with passenger airbags didn't have keys for the passenger bag... But I guess some will have.

I suppose if I bridge the two pins (17 & 18?) that should be OK regardless if the ECU is calibrated for the extra airbag but not the disable function.

Still not sure of the pin designations or the resistor value but trial and error will eventually overcome!

[xantia_v6]

The passenger airbag connects to pins 9 and 10 on the controller.

This is the diagram for early S2, but I think that it is the same system as late S1 (1996-on).

[vmaxvmax]

Great, thank you! This confirms what I thought.

Hopefully a simple job to trace and measure.

Now to unsolder the bypassed connectors to do the continuity tests...

[vmaxvmax]

I found it near to impossible to fool the ECU as my ECU 30 pin plug only has wiring for a single drivers airbag plus the two seatbelt pre-tensioners.

The way the connector plug is made up makes it extremely difficult to wire in dummy connections in order to fool the ECU.

I did indeed manage to wire in a couple of cables and fitted a 2.2ohm resistor to pins 9 and 10 but the ECU is still not happy. I did try to bridge the connectors for the passenger bag (pins 17 & 18) but no luck.

Looking at the wiring diagram, it seems that for the passenger airbag, It is not just a warning light and key switch to be bypassed as they both seem to have resistors in their circuits too.

Couldn't get it to work - might also have been a faulty secondhand unit.

Anyway, long story short, I found an expensive airbag ECU with the same numbers, fitted it and took the car to my Citroen dealer/mechanic for calibration.

They tell me that it cannot be recalibrated and the ECU is specific for a two airbag system. They say I need to get an ECU specific for a single airbag system.

These seem impossible to find on the internet. I found a couple with the same numbers but it seems the one I want may have to be one from 1995 or earlier.

Looking at the ECU's with the same part numbers it seems that the only difference might be a small square on the right of the large yellow label with the letters AG (mine) or AH etc.

I would really appreciate any help with getting to the bottom of this..

[vmaxvmax]

Help!

I am being told that the relevant part number is 9622585780 and that ECU will be specific for my one driver airbag only Xantia. This is exactly the part I have replaced twice to no avail. I am told that the Citroen diagnosis is suspect because this ECU will not prompt a missing passenger airbag fault as this ECU is configured for only the driver bag. True or not?

The mechanic says it is not possible to configure that ECU for only driver airbag.

Have done continuity tests throughout the harness, I know that the wiring and other parts of the system are fine. It is definitely the ECU.

Is it possible that the Citroen mechanic got a faulty ECU reading and, because I had replaced the unit, just assumed in error that it needs to see two airbags?

I suppose my question is really, what can the diagnostic computer say about the ECU?

I am now waiting for a third unit via eBay...


Help is gratefully appreciated!

[xantia_v6]

Taking a step back, when the airbag ECUs are read with Lexia, are there any fault codes, or is there no communication with the ECUs? In my experience some Lexia 3 interfaces have trouble communicating with the airbag ECU in 1996 and 1997 Xantias, but they can be read with a Lexia 2 or Elite diagnostic tool (if any still exist).

[vmaxvmax]

Thank you for replying!
Not sure - the mechanic was hurried though seemed positive...

The first diagnosis showed the original ECU was faulty (he said).

I replaced it with another ECU of the same part number and, as the warning light was still flashing, I assumed it to be a configuration issue. I took it back to the Citroen garage for configuration. When I collected the car, he told me that the ECU is configured for two bags and it is not possible to reconfigure.

Having been told (Planete Citroen) that the ECU with the correct part number is already only configured for one bag so it must be a faulty ECU and the garage made a wrong diagnosis I now am in doubt. The person advising believes that the code will have been C1 and that does not specify the exact nature of the fault. I don't know if this is fact or not.

[myglaren]

What happened with the 'fake airbag' resistor experiment?

[vmaxvmax]

No go! Made no difference.. I suspect that that (the first) replacement ECU was faulty...

As these ECU's are 2nd hand from breakers around Europe, I suppose the possibility of a faulty ECU is high given that many of the scrapped Xantia's may have been involved in crashes!

New ones are no longer produced.

The 'fake' airbag experiment would only be valid for an ECU designed for two airbags. It was a difficult job wiring in the extra cables to fit a resistor as my wiring loom only has cabling for the one bag and the seat pretensioners.

If it is true that ECU's with the correct part numbers should only expect one airbag, and the replacement ECU did have the correct part numbers, that would seem to imply a second faulty ECU.

The second unit was not cheap at 180€ and now the supplier is being difficult about a refund...

Fingers crossed for the third one!