MOT with Airbag light on

PaulJM

Hi,

My car has the airbag light on intermittently.
I've had it checked at 2 garages with diagnostic equipment, and there isn't a fault, so they both suggested it was a wiring problem to the actual light on the dash.
One of them messed about with the cabling under the seat and the light went off for about a year, but it's back with a vengeance now!
I've noticed that if you move the seat backwards then forwards again, this can activate the light.

This time, I'm using another mot place (offer with a service) from the place that usually manages to get the light off, so I'm worried they will fail it.
I've been told that addressing the light issue could cost a lot of money with an auto electrician.

Any thoughts

AdrianC

PaulJM wrote: »

My car has the airbag light on intermittently

It's a fail if it's on when tested.
https://www.mot-testing.service.gov.uk/documents/manuals/class3457/Section-7-Other-equipment.html#section_7.1.6
.

I've had it checked at 2 garages with diagnostic equipment, and there isn't a fault, so they both suggested it was a wiring problem to the actual light on the dash.
One of them messed about with the cabling under the seat and the light went off for about a year, but it's back with a vengeance now!
I've noticed that if you move the seat backwards then forwards again, this can activate the light.

Then not only IS there a fault, but you've already identified it... Fractured wiring to the seat (either load sensor in the passenger seat or seatbelt pretensioners) is probably the most common cause of intermittent SRS lights. And very easy to fix. Those garages need to think further than reading fault codes...

PaulJM

Makes sense, thanks.

sevenhills

PaulJM wrote: »

This time, I'm using another mot place (offer with a service) from the place that usually manages to get the light off, so I'm worried they will fail it.

Is that wise? A free MOT, they like to earn some money some how, once its failed and its on the MOT history, a friendly garage might be reluctant to pass it.
My logic is to pay the full £54.85 for the MOT, not a discounted £35 or free.

System

PaulJM wrote: »

I've had it checked at 2 garages with diagnostic equipment, and there isn't a fault, so they both suggested it was a wiring problem to the actual light on the dash.
One of them messed about with the cabling under the seat and the light went off for about a year, but it's back with a vengeance now!
I've noticed that if you move the seat backwards then forwards again, this can activate the light.

Their original claim of the reason is poppycock, the light is illuminated by the ECU sending a signal to the computer in the speedo binnacle telling it to turn it on.

As you have found out the fault is actually in the wiring where the seat is, mostly likely a broken connection or dodgy connection in the multiplug under the seat where it plugs into the car.

I've been told that addressing the light issue could cost a lot of money with an auto electrician.

Any thoughts

I doubt it will. Its a simple wiring issue and with a wiring diagram the auto electrician can narrow it down to the two, maybe three wires it is on the multiplug under the seat and even without the wiring diagram it won't take him much longer. In fact I'd be surprised if it was more than an hour's labour. It might actually need nothing more than the plug unplugging and plugging back in. What can happen is over time because of dissimilar metals on the pins and sockets in the plug itself corrosion can build up on the surface. Unplugging it and plugging it back in cuts through that and makes a good connection again. You can do this yourself although you may need to get a small socket/torx bit as some plugs secure into the socket with a small bolt.

owen_money

Tarambor wrote: »

What can happen is over time because of dissimilar metals on the pins and sockets in the plug itself corrosion can build up on the surface.

Thats a very poor design if they use dissimilar metals that allow galvanic corrosion to occur. You would have thought that the designers would have made sure the material selection would be correct to avoid this problem, seems basic to me

I agree though sometimes a clean of the connectors can work in this situation

iolanthe07

Is it a Mazda MX5 by any chance? This is a well known fault, and is often down to a shaky connection at a small junction box (relay?) under the passenger seat. It is easier to fix if you remove the seat, but you can jiggle the wires around a bit without doing that if you have smallish hands. If required, a new junction box isn't very expensive.

TonyMMM

Had this on one of my cars ... used some contact cleaner on the plug connections under the seat.. put them back together and put a small cable tie around to keep them tight. Not had a problem since

J_B

We had it on DD2's Toyota Yaris
Can't actually remember how our mechanic fixed it, but it wasn't a big problem.

Ant555

+1 for the cabling under the seat - did this yesterday.

Toyota Aygo - I noticed it and son says "Oh Yes, that light has been flashing for a couple of days"!

It has airbags in the side of the seats and I reseated all of the cable connectors under the seat and it simply went away (I suspect this is possibly what happened a year ago with the OP)

I am not sure if you are able to check yourself but it is a really, really simple thing to do as long as you are able to contort slightly and look under seat. On our Aygo the cables hang down and look to be easily knocked if something rolls under the seat or maybe someone with big feet sits in the back. If you know someone who could check this for you then I would recommend asking them - it will take 2 minutes.

System

owen_money wrote: »

Thats a very poor design if they use dissimilar metals that allow galvanic corrosion to occur. You would have thought that the designers would have made sure the material selection would be correct to avoid this problem, seems basic to me

Me too. Its been an issue in IT with sticks of RAM and motherboard DIMM sockets for as long as I can remember and it still is today. I've solved more than a few random locking up and POST failing PCs merely by unplugging the RAM and plugging it back in again. The sad part is all these enthusiasts buying "high performance DIMMs with gold plated edge connectors" don't realise they're creating a problem for themselves a couple of years down the line. I don't think the manufacturers care because as long as it lasts the warranty period, which it will, then its not their problem any more.