Technical Airbag warning light

[nigelvan]

Hi again,

2007 3.0 X250 here.
I recently replaced the passenger bench with a single seat. I put a 2 ohm resistor in place of the third seatbelt pre-tensioner to keep the airbag module happy. This worked and case closed... Today I was driving and suddenly the airbag light lit up. I assumed something wrong with the resistor so I checked that first but nothing wrong there. I then connected the original 2 pretensioners that I took of the bench. Still nothing. So I connected the pretensioner on the new passenger seat to the driver one, to rule out an issue there. Still got the light.

So I'm afraid I should look somewhere else... But the car doesn't give any codes, at least not with the generic scanning app I'm using. Multiecuscan isn't an option because it's a Citroen and I could only connect to the ECU in the past. Any clues?

 

[the green vanper]

Hello,

Have you disconnected the battery when playing around with the seats?

 

[nigelvan]

No, I didn't. But I did make sure to not manipulate the connectors while the ignition was on.

 

[the green vanper]

But it was not enough.

Probably the airbag module is damaged, there are several threads on this forum and others, it's very frequent problem while playing with the seats (when converting into campers). There are companies in the UK that can fix it. Sometimes. I assume not only in the UK.

 

[nigelvan]

But it was not enough.

Probably the airbag module is damaged, there are several threads on this forum and others, it's very frequent problem while playing with the seats (when converting into campers). There are companies in the UK that can fix it. Sometimes. I assume not only in the UK.

It's a bit strange it happens weeks after working on the seats.

 

[Zardo]

Maybe the 2 Ohm resistor had a loose contact. I don‘t know if you have the possibility to deactivate the passenger airbag in the menu with this car. If you do, you could try to deactivate it and later reactivate it. Sometimes, if a fault is no longer present, it might clear itself. I don‘t know about Citroën.

 

[nigelvan]

Was my first thought too. But it's soldered to the connector of the seat itself. No menu though, it's pretty old school. The Citroen is usually the same as the Fiat version but I noticed I couldn't connect to the other modules with MES, probably some minor config differences. I've ordered a Lexia for Citroen...

 

[the green vanper]

the third seatbelt pre-tensioner

How many airbags does your van have?

 

[the green vanper]

Sometimes, if a fault is no longer present, it might clear itself.

Airbag errors don't clear themselves When the airbag module is damaged, the error cannot be cleared with MES.

I couldn't connect to the other modules with MES

What interface are you using?

 

[nigelvan]

Airbag errors don't clear themselves When the airbag module is damaged, the error cannot be cleared with MES.

What interface are you using?

Yes they do, initially I didn't connect the new seat, of course the light came on. When I put the single seat in there together with the 2ohm resistor the light went out on its own. But yes, not all faults are the same.

I think I have only a driver's airbag, eLearn talks a lot about the passenger airbag but I think it was optional? I don't see any markings on the passenger side or even a place where an airbag could be hidden.

I've used a Vgate bluetooth OBDII dongle in the past. MES could connect to it and I was able to communicate with the Bosch ECU. I used it to diagnose a wiring fault with the high speed fan, was tricky to find. MES was unable to connect to other modules like the BCM. I figured because it must also be compatible with Lexia there must be some configuration (Address?) differences with the Fiat version.

I think if I can read at least the code then I have something to go on. I'm not so sure the module just crapped out. The light came on during a long drive on a smooth piece of road. Fiddling with the connectors is at least 3 weeks ago. I've driven the van around since then with no issues.

Now I've disconnected the battery and inspected all wiring and fuses F38 and F50. Everything seems ok. I also took off the 2 pretensioners for the bench so I could restore the original configuration (without the simulation resistance). To be clear: these pretensioners are not in the van anymore, I'm using the original pretensioner that came with the single seat. When I took off the passenger pretensioner I noticed it was already retracted. I suspect that these work with a gas charge and that you would notice when they retract. The bench is stored inside and I have no clue when or how it retracted. But I assume the airbag module won't be happy with a retracted tensioner. Maybe something happened to this vehicle before I owned it, I have no clue...

 

[the green vanper]

Yes they do, initially I didn't connect the new seat, of course the light came on. When I put the single seat in there together with the 2ohm resistor the light went out on its own. But yes, not all faults are the same.

I think I have only a driver's airbag, eLearn talks a lot about the passenger airbag but I think it was optional? I don't see any markings on the passenger side or even a place where an airbag could be hidden.

I've used a Vgate bluetooth OBDII dongle in the past. MES could connect to it and I was able to communicate with the Bosch ECU. I used it to diagnose a wiring fault with the high speed fan, was tricky to find. MES was unable to connect to other modules like the BCM. I figured because it must also be compatible with Lexia there must be some configuration (Address?) differences with the Fiat version.

I think if I can read at least the code then I have something to go on. I'm not so sure the module just crapped out. The light came on during a long drive on a smooth piece of road. Fiddling with the connectors is at least 3 weeks ago. I've driven the van around since then with no issues.

Now I've disconnected the battery and inspected all wiring and fuses F38 and F50. Everything seems ok. I also took off the 2 pretensioners for the bench so I could restore the original configuration (without the simulation resistance). To be clear: these pretensioners are not in the van anymore, I'm using the original pretensioner that came with the single seat. When I took off the passenger pretensioner I noticed it was already retracted. I suspect that these work with a gas charge and that you would notice when they retract. The bench is stored inside and I have no clue when or how it retracted. But I assume the airbag module won't be happy with a retracted tensioner. Maybe something happened to this vehicle before I owned it, I have no clue...

Yes, the passenger airbag was optionnal in the x250. Only one. As far as I remember, SEVEL added another (middle) airbag as an option only on the x290.

It's very easy to distinguish if the van is / isn't equipped with the passenger airbag, as it is installed in the dashboard and covers a small storage space (marked with an arrow on the photo):

So, not every seatbelt buckle has a pretensionner installed. But there is an electronic contact for the seatbelt reminder system. The resistor could be used for that. The seatbelt reminder system can apparently be desactivated in the menu or through MES. In my opinion (but I'm not 100% sure) it should have no influence on the airbag module.

I will try to confirm that in the technical documentation in the afternoon / evening.

You can compare the width of the driver's seatbelt tongue with the middle and external passengers' ones. They should be different according to the presence / absence of the pretensionner.

As for the naming used, I was reffering to this as I've never imagined I'd need such words in English

 

[nigelvan]

All seatbelts in mine have the same pretensioner. No passenger airbag as I have the storage space (and no SRS marking which is mandatory I believe)
The driver's buckle has two pairs of wiring, one for the pre-tensioner and one for the seatbelt reminder. the bench (with 2 passenger seats) has the same connector but this one has only two pairs, only for the pretensioners. I then bought a used driver's seat from the scrapyard and moved the driver's buckle to the other side (welded a thick metal bracket on there). I cut the seatbelt warning pair and put the 2 ohm resistor in place so the airbag module was happy and I still have 2 functioning tensioners in case of a collision. That all worked for weeks until yesterday... I guess I'll have to wait for the diagnostics tool to get the actual codes out to have a clue what is going on...

 

[Zardo]

I don't get the idea with the 2 Ohm resistor. If it's a way to terminate a CAN-bus, then (what I've read) it should be 120 Ohms. If it's to pull a 5 V TTL signal down to ground, I find the resistance quite low, too. Where did you get that value from? Much higher values should be used, in my opinion, in order to prevent the detection of a "short circuit" in the wire. But that's only my opinion, if you have good references for using a 2 Ohm resistor, then ignore this post. Or is it installed to simulate the typical current of an active pretensioner module?

Also, if this resistor sees a voltage of 12 V, it will consume I=U/R = 6 Watts of power, that's a lot, you need special power resistors for that load. Even with a voltage of 5 Volts, it will still be 2.5 Watts, a load a standard radio resistor is unable to handle. It might become hot and change its resistance.

 

[nigelvan]

I don't get the idea with the 2 Ohm resistor. If it's a way to terminate a CAN-bus, then (what I've read) it should be 120 Ohms. If it's to pull a 5 V TTL signal down to ground, I find the resistance quite low, too. Where did you get that value from? Much higher values should be used, in my opinion, in order to prevent the detection of a "short circuit" in the wire. But that's only my opinion, if you have good references for using a 2 Ohm resistor, then ignore this post. Or is it installed to simulate the typical current of an active pretensioner module?

Also, if this resistor sees a voltage of 12 V, it will consume I=U/R = 6 Watts of power, that's a lot, you need special power resistors for that load. Even with a voltage of 5 Volts, it will still be 2.5 Watts, a load a standard radio resistor is unable to handle. It might become hot and change its resistance.

I got that value from other posts, like this one, it seems it simulates the resistance an operational pretensioner module represents. I've read 2.2ohm or anywhere between 1 and 4 ohm. 2ohm killed the warning light so that was the end of the story for me. It's only a 0.25w resistor so any current would have smoked it by now. It is still intact.

I'm pretty sure it's not a CAN-bus signal as the pretensioners are directly connected to the airbag module (which in turn of course sits on the CAN-bus).
I always assumed one of the two wires to the pretensioners is ground but they both go the airbag module. Maybe those pretensioners need their metal parts grounded to the chassis. When I took the driver's seat with suspension apart to replace the foam I noticed that frame had a seperate earth strap. I didn't pay attention to that on the other chair. Maybe someone can tell me what signal goes through each pair of the pretensioner.

EDIT: scratch that earth/ground thing, if that was the case the simulation resistance wouldn't work either. Btw this is from eLearn:

Disconnect the faulty pretensioner from the wiring and connect the simulation resistance in its place.

Turn the ignition key to MAR and activate communication with the diagnostic equipment. Check whether the fault signal for that pretensioner has become intermittent

 

[RS3100]

I don't get the idea with the 2 Ohm resistor. If it's a way to terminate a CAN-bus, then (what I've read) it should be 120 Ohms. If it's to pull a 5 V TTL signal down to ground, I find the resistance quite low, too. Where did you get that value from? Much higher values should be used, in my opinion, in order to prevent the detection of a "short circuit" in the wire. But that's only my opinion, if you have good references for using a 2 Ohm resistor, then ignore this post. Or is it installed to simulate the typical current of an active pretensioner module?

Also, if this resistor sees a voltage of 12 V, it will consume I=U/R = 6 Watts of power, that's a lot, you need special power resistors for that load. Even with a voltage of 5 Volts, it will still be 2.5 Watts, a load a standard radio resistor is unable to handle. It might become hot and change its resistance.

Each monitored circuit in the CAN bus has a small resistance, which is monitored by the ECU that controls it's connected equipment. If the resistance changes outside of specification, that is what sets a specific fault code related to the circuit. High or low resistance can obviously indicate a poor or broken connection.

If you remove a monitored component from the SRS system for instance, you need to replace it with a compatible resistor to simulate the specified normal resistance in that component's circuit, otherwise you will have a fault that triggers the warning light, which you will not be able to clear.

For instance , the fault B1B03-1A will be set if the driver's airbag first stage circuit resistance is below the monitored threshold, and B0103-1B will be set if the resistance of the same circuit is above the threshold.

But there are numerous fault codes that might be triggered for various fault conditions in the SRS system, each of which will trigger the fault warning light. Without knowing the codes stored, diagnosing the fault is like looking for an invisible needle in a haystack unless there is a blatantly obvious problem such as a broken or damage wire.

I believe AlfaOBD may be able to read Citroen Relay ECUs more successfully than MES, although I haven't tried personally as I've never needed to. You won't be able to retrieve SRS or indeed fault codes from most other systems with a generic OBD app. They only show drivetrain fault codes. You need either a dedicated all systems scanner for the make of vehicle you are attempting to diagtnose, or a multi-vehicle scanner which has either all system capability, or some of the cheaper ones will just read ABS, SRS and perhaps a couple of other system faults.

 

[nigelvan]

Each monitored circuit in the CAN bus has a small resistance, which is monitored by the ECU that controls it's connected equipment. If the resistance changes outside of specification, that is what sets a specific fault code related to the circuit. High or low resistance can obviously indicate a poor or broken connection.

If you remove a monitored component from the SRS system for instance, you need to replace it with a compatible resistor to simulate the specified normal resistance in that component's circuit, otherwise you will have a fault that triggers the warning light, which you will not be able to clear.

For instance , the fault B1B03-1A will be set if the driver's airbag first stage circuit resistance is below the monitored threshold, and B0103-1B will be set if the resistance of the same circuit is above the threshold.

I can confirm that the fault clears itself in the case of open circuit. When I switched seat I forgot to connect the connector and had the airbag light on. Once restored it went out after about 10 sec of running the engine. This might of course not be the case with all airbag related codes.
That was 3 weeks ago, now it went on for no obvious reason (while driving on a straight piece of road)

 

[RS3100]

I can confirm that the fault clears itself in the case of open circuit. When I switched seat I forgot to connect the connector and had the airbag light on. Once restored it went out after about 10 sec of running the engine. This might of course not be the case with all airbag related codes.
That was 3 weeks ago, now it went on for no obvious reason (while driving on a straight piece of road)

Without retrieving a fault code, you are looking for a needle in a haystack, as I say. It might be something simple, but B0100-49 is a fairly common fault on Sevel vans, which means a fatal internal error inside the SRS ECU. That is the one which companies such as Crash Data or Northern Autotech might be able to repair depending on the condition of the ECU when they examine it. Without a code or obvious visible fault though, you are blind!

There are over 100 different conditions that can set the SRS fault warning light.

 

[nigelvan]

Yes, I am aware I'm flying blind. I was hoping it would be something simple like a loose connection. I'll wait for the Lexia/Diagbox dongle to get the right code.
I'm not from the UK but I already found some local companies that respond to this code, should a fried SRS ECU be the case. Would a second hand unit be another option?

 

[Zardo]

If investing in an OBD diagnostic system, get a decent tester which is actually able to read the codes, clear the codes and do the checks (ideally with the ability to connect to each Node on the CAN bus, not only the ECU). Sometimes faults can be stored in a CAN node and the ECU and both need to be cleared.

 

[RS3100]

If investing in an OBD diagnostic system, get a decent tester which is actually able to read the codes, clear the codes and do the checks (ideally with the ability to connect to each Node on the CAN bus, not only the ECU). Sometimes faults can be stored in a CAN node and the ECU and both need to be cleared.

There seems to be some confusion over the meaning of ECU. It can mean electronic control unit or engine control unit. When I said SRS ECU, I meant of course the Safety Restraint System electronic control unit, not the SRS and Engine ECUs (nodes).

I've never come across a vehicle where the same fault code is stored in more than one control unit. To read faults in the SRS ECU on the Ducato, you need to connect directly to the SRS ECU, you won't find them stored anywhere else. Body system faults will be found in the BCM, engine faults in the ECM etc.

AlfasOBD is somewhat unique as you have to physically connect it to every ECU on the vehicle separately, read and if necessary clear codes from each of them in turn. MES can also work that way, but you can also start a full system scan which discovers every ECU/node on the vehicle and lists any faults present in each of them (but you need the CanTieCar or vLinker MS VCIs to be able to do that, because otherwise you have to add or remove adapter cables to connect to various busses) and you can also clear them all at once if required. That's also how most independent aftermarket diagnostic scanners work.