Can an airbag be disconnected in a 'conforming' way?

ThisIsWeird

Hi.

Situation is that a colleague has had an intermittent airbag/tensioner warning beep on start-up. It can be ok for a few weeks, but then returns.

At the last service, he asked the garage to run a check on it to find the guilty party, and it's one of the side curtain 'bags which shows 'open circuit' - which most likely would mean either 'faulty wiring, or a failed igniter'. They are currently getting a worst-case scenario quote for the repair.

I know that a faulty airbag is an MOT failure, but also know that they can be disabled, say following activation, if the owner didn't want the cost of replacing it. What I don't know is if this is 'legal' - against regs.

Due to the value of the car, they are considering this option should the replacement cost be anything close to 'write-off' or 'seriously not worth it' level.

Q - does anyone have definitive info on whether what I've said is correct - it's 'ok' to ECU-deactivate an unwanted/used airbag, thereby removing the warning signal, and continue sans that 'bag? Ie, all other 'bags still active.

Thanks.

Mildly_Miffed

Program the ECU to believe that bag is still working correctly? It might be able to be done, depending on the ECU. But it's not going to be straightforward.

It's often easy to fool the ECU - it's commonly done on vans when a double passenger seat is swapped for a single, so the ECU's looking for a missing belt pretensioner. A resistor in the plug can do the job.

But that's slightly a different question, because you're removing something that simply isn't needed, since the seat it goes with is no longer there. This is an airbag that's still fitted and would still provide occupant protection in an impact, but which you want to work around because it's broken, instead of doing the proper job and mending it. Is it simply a loose plug...?

Mr MOT will fail it for airbags "OBVIOUSLY MISSING" or "OBVIOUSLY INOPERATIVE".
https://www.gov.uk/guidance/mot-inspection-manual-for-private-passenger-and-light-commercial-vehicles/7-other-equipment#section-7-1-5
Neither of those will apply here, because the bag hasn't deployed, so the trim isn't ripped apart.
So as far as Mr MOT's concerned, if the light self-tests normally, it's a pass.

Whether it's a breach of C&U, or whether his insurance will object if notified, are different questions entirely.

paul_c123

ThisIsWeird said:

I know that a faulty airbag is an MOT failure, but also know that they can be disabled, say following activation, if the owner didn't want the cost of replacing it. 

You'll have to explain this one a bit more clearly. An airbag is a use-once thing, once its activated it won't do it again!! it WILL record the "crash data" in the airbag module and on some cars a level 2 or 3 diagnostic computer can reset it* (ie a DIY proposition), and on others its more complex and there's specialists who you'd need to send the module off to, or replace with a virgin module and possibly need to code it to the car.

*reset would remove the crash data event, but you'd also need to replace the airbag. There's no option to NOT replace the airbag but clear the fault code and prevent the airbag light coming on on the dash. Unless you know different, of course.

ThisIsWeird

Thanks, both.

I don't know better!

But, I had a C3 Picasso in the past which was a Cat N car - which I knew - and which had an activated pre-tensioner - which I ditto (and possibly an ignited curtain bag, I'm trying to recall - there were two wee cuts in the headlining immediately above the driver's window.) Anyhoo, these had clearly been 'removed' from the sensing system, as the car would do its usual 'airbag' checks on ignition, and would go out once the remaining 'bags had primed - it wasn't bothered about the pre-ten. I was happy with that.

What I don't know is if that 'conformed'. I assumed it did, and it never failed an MOT on this issue - the tensioners were clearly activated - the receiving clip was an obvious inch lower - and it wouldn't have taken much to spot and suspect the headlining cuts either. But, perhaps it was just missed each time? No idea.

The passenger side airbag can obviously be isolated using the normal switch, but that doesn't deactivate the warning. So the Q remains - is it an option to tell the ECU to 'ignore' the faulty 'bag, and would that be 'ok'?  As it is in a 2 to 1-seat van conversion.

I suspect it's very doable, but have no idea whether it's non-conforming.

paul_c123

Its theoretically do-able but no company will do it for you and I imagine you don't know how to do it yourself.

The Cat N sounds like a bodge - if the airbag has been bodged, what else has? Don't forget, the MoT is a non-invasive check looking at the car, not inspecting components properly or plugging in/interrogating diagnostics etc. So its not as thorough check as may seem. Someone must have deliberately thought it was okay to do away with pre-tensioners and some airbags and to sell it on.

ThisIsWeird

paul_c123 said:

Its theoretically do-able but no company will do it for you and I imagine you don't know how to do it yourself.
The Cat N sounds like a bodge - if the airbag has been bodged, what else has? Don't forget, the MoT is a non-invasive check looking at the car, not inspecting components properly or plugging in/interrogating diagnostics etc. So its not as thorough check as may seem. Someone must have deliberately thought it was okay to do away with pre-tensioners and some airbags and to sell it on.

I don't need to imagine that you don't know either

I could do it myself, but I'd need the equipment. Everything else you've said is speculation, including your thoughts on my ol' Cat N. But I knew exactly what I was buying, and it served me well for 6 years. I sold it on - as described - for less than half the 'usual' price. Last checked on DVLA - it's still going.

Best bodge evs.

chrisw

As hinted above, a 2 or 3 ohm resistor will put out the airbag light assuming it's the airbag rather than the wiring that's faulty. Of course, you will then no longer have a functioning air bag. 

It's not illegal as such, indeed companies like Momo offer them so you can fit their non-airbag steering wheels. Whether the insurance companies have a view is another matter.

Iceweasel

MOT Manual
7.1.5
An airbag that is switched off is not a defect.

But: obviously missing or obviously inoperative is a 'major' fail.

Mildly_Miffed

chrisw said:

It's not illegal as such, indeed companies like Momo offer them so you can fit their non-airbag steering wheels. Whether the insurance companies have a view is another matter.

With a caveat of "off-road use only".

Mildly_Miffed

Iceweasel said:

MOT Manual
7.1.5
An airbag that is switched off is not a defect.

But: obviously missing or obviously inoperative is a 'major' fail.

That's referring to passenger dashbags with a key switch to render them safe for child seats.

paul_c123

You don't need an airbag on a car. Until you need it.