Dallas, I'm no audi mechanic, but here's my thoughts on this. Maybe your aftermarket cats aren't up to the spec of the audi units and aren't removing enough of the bad emissions, so they are still tripping the 02 sensors and making them throw the codes. I hope that's not the case since you just spent big bucks on them.

Does the car run fine?

There is some diagnostic software that comes highly recommended called Vag-com. Check it out at:
http://www.ross-tech.com/Merchant2/m...ry_Code=VAGCOM
I hear its better than the diagnostic toolsthat Audi supplies to their dealers. I think it can clear codes andit gives descriptions ofwhat your codes mean so you don't have to go look them up. You should install the software ona laptop and put it in the car. It hooks into the cars computer with a special cable.

Its worth checking out. I plan on buying it. Good luck.

PS Please let all of know what kind of a solution you come up with for this problem.

Paul.

 

Igot a newcat for a 96 A6 for about $600from the guys at Force Five in Concord NH. 603-223-6700.

Sorry to sound like a broken record [X(]- but Chris at Force Five has been a big help. [:-]Without his low prices on new parts and the ability to get used ones from him, I would have been forced to switch to fords or some other bottom feeder like a Honda, Toyota, or Lexus. [:'(]

 

Hey now, I owna ford! Besides, Dodge should have been at the top of your bottom feeder list.

 

On my A6 Avant, I have been getting these same codes since at least 80K in 2004. P0421 (Pri Cat Bank 1), P0431 (Pri Cat Bank 2), and P1423 (secondary air flow too low bank 1) always show up 1 or 2 days after being cleared.

I can guarandamtee you these cats did not go bad at 80K.

How to know? I always knew those emissions tests in Denver would be good for something. In 2004 at 66K, my hydrocarbons were 0.07 gm/mi and NOx was 0.2 gm/mi. In 2006, at 136K HC were 0.13 gm/mi an NOx 0.3 gm/mi. Pass/fail cutpoints are 1.2 for HC and 3.0 for NOx. This car is pretty darn clean from an emissions standpoint.

If the cat was shot, HC would be much higher, trust me, people I know who have had bad cats have failed the emissions test hands down. Even if my cat is bad, why would I replace it if my car runs that clean? That makes no sense.

I need another emissions test this year (177K) so will do that before taking to my mechanic this week. I will try to have him do a pre- post- cat temperature reading.

The fuel economy on this car has always ranged from 20-22 mpg, so I don't believe it is an O2 sensor. I believe it is a secondary air leak issue that is of very minor concern (except for that damn CEL/MIL[:@]). Hope to have a diagnostic on that this week.

Will let you know what transpires.....

 

I love your gurantee about the cats at 80K. If you really believe that I'll give you a gurantee that the land I'm selling 2 miles east of Miami is dry.

I believe your real problem is the secondary air pump. It usually takes a few days for it show up after being reset. The cat errors are probably coming along for the ride -- but you might be seeing a sensor problem.

 

Do you have any details on this reflash? Is there a bulletin numbered C260503?

I have an '02 A6 2.7T and just started getting the P0421 error. I'd really rather not buy a new cat (<7 yrs old but 110k miles).

 

Anyone?

 

Way late, but for all the 'searchers' finding this:

I have found on two other cars I own, not Audi but still, this code and/or 'efficiency code' were thrown up due to CRAP GAS. Dont know what was in it, but I was going to the 'cheap' guys for awhile and this code came up... both cars. I drove this way for months 'cause I'm not in an emissions area until a bad experience made me switch stations.. guess what? With-in a day code gone and has not returned... so switch to good gas or a different station for a tank and see before changing the cats.

 

Dealer only procedure. It will cost you about $350. I forget the version number, but you can check to see if you have the latest version with VAGcom. Info is floating out there somewhere.

 

Why not just spend the money on tuner software?

Or is the dealer flash covered for some models. (like my MY 2000 A6 2.7T)

Not clear to me what to do first if you have the P0421 error code?