Airbag light problem - 2000X A4 2.5TDI avant Quattro tiptronic

[Alibi]

Every morning I start my car and the airbage light goes out but comes on a few seconds later. I then stop the engine and use an airbag resetter tool to put the light out (sometimes takes a couple of attempts). Thereafter the airbag light works fine all day, but the next morning I have to go through the same procedure. recently when the car was in getting a new diesel pump (£785!!) and two new rear springs, I asked the garage to sort the airbag problem. They ran a fault code check which said there was a fault with the ECU and they couldn't switch the light off, upon which I plugged my wee box in and switched it off. It appears to me that the fault probably isn't in the ECU as it works OK once I fix it but the fault reappears overnight. Having spent about twice the value of the car in repairs in the last year, I am loath to scrap it for this one last problem, but I can't really sell it although I can get an MoT if I switch the light off in the morning before it goes for its test. Can anyone shed any light on what the most likely problem is? Also, to get a peek at the ECU I think I need to remove the ashtray - where do you press to release it? Does the climate control panel have to come out first, and if so how do you do that? I have a feeling I have already done that in the past but can't remember what holds it all in.

I think I'll ask them to re-run the fault code check and get a full list of the actual codes as that might give a further clue. i just don't think the ECU is the problem when it can be persuaded to work fine fairly simply, but I can't figure out what might change overnight to stop it working other than maybe some sort of voltage drop or condensation forming.

 

[S4_dan]

Check the connection under the drivers seat. If the seat has been pushed right back this can cause the connector plug to come undone. Could be in your case loosely undone and causing intermittent faults.

 

[aragorn]

Its probably a faulty airbag ECU. the memory chip inside them starts to die i think, and they get worse when cold, hence leaving it over night causes the issue to recur.

Use proper VCDS to read the error code and if its the 65535 checksum error code then you need a new airbag module.

 

[Alibi]

Check the connection under the drivers seat. If the seat has been pushed right back this can cause the connector plug to come undone. Could be in your case loosely undone and causing intermittent faults.

I've already done that and it seems OK at the connector. Also gave the connectors a scrape in case they were corroded but they seemed OK. Haven't done the passenger side yet. however the garage didn't pick up a fault code that would indicate a connector problem, just an allegedly faulty ECU which I suspect is not actually the case.

The car has had problems in the past with the electrics due to water getting in and flooding the gearbox ECU although I sorted that by stripping it and brusing with a hush puppy brush. also had a problem with the throttle sensor, again maybe linked to water. My first thoughts were that the airbag problem was likely to be connected to water getting in somewhere but the ECU location suggests it's not likely to get wet itself.

 

[Alibi]

Its probably a faulty airbag ECU. the memory chip inside them starts to die i think, and they get worse when cold, hence leaving it over night causes the issue to recur.

Use proper VCDS to read the error code and if its the 65535 checksum error code then you need a new airbag module.

Thanks for that. I am keeping an eye on Ebay although I have mislaid the exact part number and so may have to open it up to check - it's the standard number but can't remember the final suffix apart from that it is 2 letters, possibly one of them a T. The Audi dealer refuse to give out details of the part number as they don't want anyone buying a secondhand one.

Maybe should fit an electric heater with a froststat...

 

[aragorn]

does your car have curtain airbags?

 

[aragorn]

If not the original part was 8D0959655J and the current replacement part is 8D0959655TD

 

[Alibi]

That TD suffix rings a bell. Pretty sure it doesn't have curtain airbags. Can either part number be used then? I assume the TD suffix was an updated version, possibly to correct some sort of problem with the original?

 

[aragorn]

yep, most cars have J unless its been changed.

 

[Alibi]

That's interesting - mine has a TD suffix so might have been replaced previously (I have had the car since 2006).

I have sourced a J suffix from a local breaker - £40 + VAT. Will give it a go and see if it makes any difference. If the same fault persists it would tend to indicate that the ECU is not the problem. I could get a TD but they are about 4 times the price so worth a try with the J. My local Audi independent specialist says they can recode the unit if necessary.