Airbag – ecu – configuration error 401

[hogweed]

Originally Posted by stevestrat

Eventually it came back to haunt me again so went down the solder/heatshrink route but added 6" of wire all round so that seat movement wouldn't be a problem. Ended up doing the same with the 260.

Yeah I've already done that. Just one thing though... since my last question I've read some posts saying that polarity matters with the two wires to the pretensioner?


Having read endless ones which said it didn't, I failed to pay attention to which wire was which when putting the new connectors in... maybe I'll have to turn them round and try again

[stevestrat]

Pre-tensioner and airbags are simple circuits, polarity doesn't come into it.

[hogweed]

Originally Posted by stevestrat

Pre-tensioner and airbags are simple circuits, polarity doesn't come into it.

Yes, that's what I would have thought. Trouble is, when things go wrong for apparently no reason, you start to question your logic, and a couple of people have posted here that they discovered the pre-tensioners WERE polarity sensitive, then I noticed that the wires out of them are differently coloured (something like white/purple and white/black - can't remember now), so I thought maybe it was true... heigh ho.

[Jamiewelch]

Originally Posted by hogweed

Just one thing... if I decide to do some resistance testing of modules (battery disconnected obviously), do I risk damage/accident?


I'm thinking specifically of the pre-tensioners - could the current from the meter fire them ?

Do not measure the resistance of anything that can fire. The voltage applied to perform the resistance measurement could fire the airbag / tensioner.

Did you disable the tensioner in the airbag ecu though? In the first post you said that you did, and then in post 12 you said nothing has been altered. Best bet to find the fault is to use a T4. But remember in a MK2 setup the pretensioners are wired in series which is why the T4 only says it is a front pretensioner and can't give a side. There is a polarity, but it shouldn't make any difference as it is a simple resistance measurement.

[hogweed]

Originally Posted by Jamiewelch

Do not measure the resistance of anything that can fire. The voltage applied to perform the resistance measurement could fire the airbag / tensioner.

Thanks Jamie, that’s what I wanted to know. I’ll leave them alone.

Originally Posted by Jamiewelch

Did you disable the tensioner in the airbag ecu though? In the first post you said that you did, and then in post 12 you said nothing has been altered.

Sorry if I didn’t explain clearly. What happened was this: a few weeks ago, I moved the driver’s seat, and the light came on, having been off for maybe 2 years (I never normally move the seats). I assumed moving the seat had broken a dodgy connection somewhere under the seat (always the case previously), so I decided to try using the little SRS Tool (supplied by the same people as TOAF, but a separate module) to see if I could find where the fault was – it said pre-tensioner high resistance, if I remember correctly.


Then I noticed that you could toggle various sensors etc on and off – as I did this with the pre-tensioner, the airbag light switched on and off. I left it toggled off as it annoys me when it’s on, and I knew it would be weeks before I could get an appointment with the T4 man.


Then the car developed a fault with the gear selection, so I took it to a local garage. He’s a lot smaller than me, so I found the seat had been moved forward when I picked it up again, and the light was on yet again. This time SRS Tool told me I had high resistance on left and right ITS, whatever they are, and an ECU config error.


I re-enabled the pre-tensioner sensing to set everything back to default, but the errors remained.


I remade the pre-tensioner connectors I’d soldered years ago, thinking I might have a dry joint, but it made no difference.

Originally Posted by Jamiewelch

Best bet to find the fault is to use a T4. But remember in a MK2 setup the pretensioners are wired in series which is why the T4 only says it is a front pretensioner and can't give a side. There is a polarity, but it shouldn't make any difference as it is a simple resistance measurement.

Yes, thanks, that explains it. I’ll get it booked in, but it’ll likely be up to 6 weeks before I can get to see him…


I don’t know if the SRS Tool is capable of corrupting the airbag ECU – it seems a very simple app for reading/clearing the codes, and toggling sensors on and off – can’t really do anything else.


But what do I know

[hogweed]

Well, that was educational. I threw myself on the mercy of Mark, our T4 man, who saw me despite being booked up for weeks, and was surprised when he used the same little SRS tool that I had… I asked why he didn’t use his T4, and can’t remember the exact answer, but I think the words “slow” and “agricultural” featured.


About 30 seconds later, no airbag light, no errors. Explanation as follows:


There must have been a pre-tensioner wiring fault under the driver’s seat, as moving it was what had brought the light on. When I re-did the connectors there, I reset all the sensors etc to default using the SRS tool… and this was where I went wrong.


I had mistakenly enabled what Mark called the “curtain” airbags… and my car doesn't have them, thus the high resistance errors, and the config error. Disabling the bags which aren’t present turned the light off – simple as that.


I feel a bit of a plonker, but glad the Rover lives to fight another day

[SD1too]

Originally Posted by Jamiewelch

Do not measure the resistance of anything that can fire. The voltage applied to perform the resistance measurement could fire the airbag / tensioner.

I've read that warning too but I doubt it Jamie. The DCU applies a test current of < 40 mA to check circuit continuity. The current used in multimeters to measure resistance is deliberately miniscule and most likely well below that figure.

Simon

[Jamiewelch]

Originally Posted by SD1too

I've read that warning too but I doubt it Jamie. The DCU applies a test current of < 40 mA to check circuit continuity. The current used in multimeters to measure resistance is deliberately miniscule and most likely well below that figure.

Simon

I know it shouldn't, but I don't want the blame if someone has a multimeter that isn't as well made and their airbag pops

[hogweed]

Originally Posted by Jamiewelch

I know it shouldn't, but I don't want the blame if someone has a multimeter that isn't as well made and their airbag pops

Well, you cetainly put the fear of God into me


Which, given my propensity for "trying things", was probably no bad thing...


Fortunately, for me, it's not longer a problem


For now...