Side airbag light won't go away

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johnny625
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My Cars: Citroen Xsara 1.9 td
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Side airbag light won't go away

Post by johnny625 »

Hi folks,

I am having yet another nuisance with my Xsara. Its a mk1 1998 1.9 td. Now the main air bag light goes on ignition and goes off as normal after a few seconds. The side air bag light does the same but after only a few seconds comes on steady and does so while I drive and until I turn of the car.

I have a sneaking suspicion that its a matter of poor electrical contact on some plug somewhere and I gave the connectors under the front seats a good clean. This didn't turn off the light.

I also found the air bag ecu which is located in front of the gear lever and gave its main plug a spray of contact cleaner of course after disconnecting the battery and waiting for about 15 minutes. This also didn't fix the light.

Now do MK1 Xsara's have a separate side airbag ecu also. If so where it is located?

I am fairly knowledgeable in electronics/electrics but I am kind of worried of omming the side air bag wiring with a multimeter. I am concerned that it might set off the air bag or the pyrotechnic belt tensioner.

The VIN is:

VF7**************[VIN obfuscated, can be read by forum staff]


Can someone point out to the location of side airbag module if it even exists on this car?
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Re: Side airbag light won't go away

Post by xantia_v6 »

I am not 100% sure about the Xsara, but there are probably side impact ECUs mounted in each B-pillar near the bottom, possibly accessible by removing the front seatbelt reels. It is probably worth some effort to get a Lexia reading of fault codes, to isolate the problem.
johnny625
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Re: Side airbag light won't go away

Post by johnny625 »

Actually I have ordered a Lexia and the associated cabling from Ali-express and I expect it to arrive in a couple of weeks. Now the thing is in my city there is only one, yes ONE garage that has a proper, working Lexia setup which can talk to my car. I have tried on many other places it seems they can't connect with the car electronics at all. Apparently in the late 1990's Citroen used a specialty protocol which was non standard and it can't be read with a normal OBDII scanner.

Due to the issues from above, I decided to order Lexia myself. The only garage that has a proper Lexia is booked for a week in advance so I guess I am just going to try spraying every connector related to the pretensioners and the side airbags with contact cleaner and maybe bend some metal connectors slightly so they make a better contact. I know that soldering the wires directly is an option but that seems too extreme to me. Sometimes I might need to take the seats out and I don't want to cut wiring to be able to do that.
johnny625
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x 5

Re: Side airbag light won't go away

Post by johnny625 »

Glad to inform you that I have fixed the issue. After spraying every orange cable connector with a contact cleaner near the air bag ecu and giving the under seat connectors a slight bend in the pins, the light is gone. I hope it will stay off for a while at least. Fingers crossed.


I have working theory about why airbag lights seem to stay on often in Cits and Pugs. The air bag and the pretensioners squibs have a low resistance, on the order of one ohm or less. The air bag ECU seems to measure this resistance on every ignition cycle and if its too high it keeps the air bag warning lights on.

From my experience with electronics I know that when you try to measure resistances close to one ohm or less contact resistance plays a huge role. When you factor in the dirt and dust that gets under the seats its easy for the under seat connectors to develop a notable amount of contact resistance which is added to the resistance of the squib. This is registered by the air bag ecu which lights the warning lights. Now I don't know whether this extra resistance will prevent the air bag from opening in an accident but better be safe than sorry I guess.
Ricardo
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Re: Side airbag light won't go away

Post by Ricardo »

johnny625 wrote: 18 Sep 2017, 21:30 Glad to inform you that I have fixed the issue. After spraying every orange cable connector with a contact cleaner near the air bag ecu and giving the under seat connectors a slight bend in the pins, the light is gone. I hope it will stay off for a while at least. Fingers crossed.


I have working theory about why airbag lights seem to stay on often in Cits and Pugs. The air bag and the pretensioners squibs have a low resistance, on the order of one ohm or less. The air bag ECU seems to measure this resistance on every ignition cycle and if its too high it keeps the air bag warning lights on.

From my experience with electronics I know that when you try to measure resistances close to one ohm or less contact resistance plays a huge role. When you factor in the dirt and dust that gets under the seats its easy for the under seat connectors to develop a notable amount of contact resistance which is added to the resistance of the squib. This is registered by the air bag ecu which lights the warning lights. Now I don't know whether this extra resistance will prevent the air bag from opening in an accident but better be safe than sorry I guess.



Excellent info! I have heard plenty of that regarding the Cits and Pugs.
Cheers for that, Johnny!
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Re: Side airbag light won't go away

Post by Ricardo »

Got this proclem solved, as well. It seems, indeed, that the erratic airbag light is caused by the wiring loom. I replaced the connections, and loosened all of the cables under the driver´s seat. Also, the thicked cable and another smaller wire connection to the seat/side airbag was run very, very tightly between two steel rods on the back of the seat.
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Re: Side airbag light won't go away

Post by wheeler »

johnny625 wrote: 17 Sep 2017, 21:53
Now do MK1 Xsara's have a separate side airbag ecu also. If so where it is located?

Just to answer that question, it depends on the age, the early models had a separate ECU for each lateral airbag, it was a metal casing & just looks like a half sized normal airbag ECU, the airbag was connected directly to it & it also detected the impact, this ECU detonated the airbag directly. It was bolted to the inner sill near the B pillar.
I would imagine being a 98 model this is the setup you would have.

Later models had a single central airbag ECU & all the airbags are directly connected to it, In the inner sills there are basically just little impact sensors known as satellites which are connected to the central airbag ECU.
Something like this
Image
Vuk1987
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Re: Side airbag light won't go away

Post by Vuk1987 »

Today, I removed driver seat on my Xsara Picasso and I accidentally severed airbag cables that are below the seat. I noticed that one of the previous owners removed the connector (plug) and connected wires directly using only tape (that's why it was severed that easily). Unfortunately i didn't expect that to happen, so I haven't looked at connections to find out which wire connects to which. On the seat side there are yellow-green wire, and than in orange shield there are brown and blue wire. On the floor side there are yellow-green wire, orange and yellow wire. I would appreciate very much if one could tell me how wires should be reconnected.
Thanks in advance
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Re: Side airbag light won't go away

Post by GiveMeABreak »

Ok you'll need to post your VIN up here and I'll look at the wiring for you - can you confirm that you are talking about the left hand seat (driver's side) left hand drive?
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Vuk1987
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Re: Side airbag light won't go away

Post by Vuk1987 »

My VIN is: VF7**************[VIN obfuscated, can be read by forum staff]
It is a left seat, a driver seat on a left wheeled car (continental part of Europe).
I can post pictures if necesary.
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Re: Side airbag light won't go away

Post by GiveMeABreak »

A photo might help identify the right plug. Here is the complete airbag diagram for your Picasso.

Image
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Re: Side airbag light won't go away

Post by GiveMeABreak »

Here's most of the codes for the equipment on the Wiki. They are sorted in number order to make it easier to locate.
https://frenchcarforum.co.uk/wiki/Elect ... ring_Codes
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Vuk1987
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Re: Side airbag light won't go away

Post by Vuk1987 »

Thank you very much for the diagram, I have found the circuit, it is from the central unit 6570 traces 6507 and 6506 go to bottom right to traces 6507 and 6508 to the unit 6563, but I'm don't have enough knowledge to figure out from there which are the color codes.
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Re: Side airbag light won't go away

Post by xantia_v6 »

Can you look under the passenger seat? the colour pairings might be the same.
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Re: Side airbag light won't go away

Post by GiveMeABreak »

Double check the wiring sleeves - sometimes they have the 4 digit number printed on the sleeve.
Wires
6508: Passenger side airbag + command
6507: Driver's side airbag - command

Whatever you do, make sure the battery is disconnected and wait 10 minutes before doing any work on the airbag circuit, to allow the capacitors to discharge in the airbag control units (risk of setting them off when playing with wiring).
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