cat failure 3.0 Quattro (again!)

[sparkyunlimited]

Hi all....
I have just purchased an A4 3.0 quattro.

1 day after purchasing the CEL came on.

I have just had it checked by my mechanic and it would appear that the pre-cats on both banks have failed.

the emissions are still perfect and the engine runs perfect.

So.. rather than spending hundreds of pounds on 2 new cats (well.. 4 actually) does anyone know if there is a way of getting the ECU re-programmed to ignore the signal from the lambda for the pre-cats?

I guess the last resort would be to replace both pipes with cats - which is apparently a P.I.T.A... what kind of labour time and money would I be looking from a private garage?

By the way.. the car has done 161,000 miles and is still on its original exhaust and cats!

cheers
Dave

[iwaters]

What were the fault codes? How is the mechanic so sure it is the pre cats? The pre cats are there to help reduce emissions during a cold start whilst the main cats warm up. The lambda sensors are downstream of the main cats so are not really monitoring the efficency of the pre cats.

No you can't tell the ECU to ignore the lamda sensors. They are fundermental for the enigne to run at the correct air fuel ratio and for ensuring the emissions are kept in check. Even if you could get the ECU to ignore it you would never pass and MOT.

[sparkyunlimited]

when it was on the computer he checked the outputs from the lambdas - they were all reading and fluctuating when the engine was revved.. two of them had high voltage readings and the other 2 had low voltage readings - apparently they should be the same or something?? there wasnt fault "codes" the bosch reader said that both the pre-cats were not working. As I said above, the actual emissions were perfectly normal on CO, LAMBDA and HC.

Something else I should mention was that the previous owner said that the EML had come on before xmas - with the pre-cat being at fault - he reset the EML on the computer in the garage where he works and ran the car on superunleaded - (he had briefly swapped to regular prior to the light coming on) and the light stayed off up until I purchased it on Saturday... Dont know if that was pure luck though!?

[iwaters]

The front lambda sensors should switch voltages between 0.3 and 0.7 a few times a second. The rear sensors should remain steady at around 0.7 0.8V although they will fluctuate slightly. Anything outside of these ranges will indicate a problem.

Diagnosing lambda and cat probelms can be hard. I have an outstanding problem on my car which could be the cats. My emissions are fine so until it fails an MOT I'm not going to bother fixing it.

If the CEL is on there will be codes lodged. I suggest getting or finding someone with VCDS to check again.

The pipes with the main cats are about £900 each, and that doesn't include the pre cats so you want to be damm sure they need repalcing before doing that!!

Changing between super unleaded and regular isn't going to make any difference.

[sparkyunlimited]

Two fo the readings were definitely fluctuating between the 0.2/3 and 0.7/8 area but I seem to recall that the other two were higher than the 0.7-0.8... more like 1.2 I think. I have done about 20 miles since the light was reset and it isnt on..YET. I am thinking that the guy that sold it to me might be telling porkies about it only happening once to him.. it may well be the reason he has sold it with such a big repair bill in sight having spent over £2k getting a top end rebuild on it 20k miles ago after the bolt holding one of the cam sprockets sheared off!

I suppose if the light continues to come on periodically I have 2 options.. buy a reader and reset it every time it does or take the bulb out! :s

[iwaters]

I think, although do not for sure but the light panel is a LED panel and you can't remove the bulb. Doing this is anyway can be a bit of a gamble because if it comes on again for a different error you wont know.

A VCDS cable off ebay and the shareware version will only set you back less than a tenner, assuming you have a laptop or a long USB cable! That will do fine for switching off the light. Althoguh double check it will work with you car because I think it all changed arougn 2004-2005.

[sparkyunlimited]

I was wondering if they might be LED... I have a long history with BMW which are LED..

I have seen the hand held scanners for about £30-£40 on ebay.. that might be the way forward so it can be left in the car.

Bloody Audi's LOL... I should have stuck with BMW! although I do love the way the Quattro drives, its alot more sure footed than even the M3's I have owned.

Thanks for your comments though :o)

[sparkyunlimited]

The light came back on after about 60 miles.... time to purchase a unit to reset the light myself!
Message to Monkey117SE - sorry mate, I cant PM until I have 10 posts! :s Mine is an auto which is still shifting up and down perfectly at 161k... it had an oil change at 140k. The only transmission thing i have that is weird is that when manouvering at low speed it feels like the diff is working against turning - dont know if it is an LSD thing?? My old M3 used to do something similar when it needed the diff oil swapping but the diff oil was done at the same time as the transmission fluid on my quattro... it might just be a quattro thing!???