If I had just known about this forum 6 months ago!!

I've had the same code. I bought my '03 A6 3.0 just a few months ago with 85K on it. Great car, great styling, better mileage than I expected. Overall I've been happy. However, a few weeks after buying the car the P0421 CEL code came up. I took it to the Audi dealer in Dallas who quoted $1600 to resolve the issue. In reading your post, I discovered that federal law which OF COURSE I just missed by 5K miles. Just my luck!

So to ensure I read everything correctly (and yes, AudiTech I did search, haha), either the cat needs to be replaced or it could be a bad O2 sensor?

Did 1600 sound high to you to resolve the issue?

What would a O2 replacement run? Perhaps I could try this less expensive alternative to see if it resolves the issue.

Anyway, I really enjoyed reading your post. Tasted any good water lately? That was funny...

Thanks, Collin

 

Yeah that sucks! Since your over 80k miles your gonna need that new cat converter, the cat itself costs over $1,000 and labor is around 4 hours, so i would estimate it at around $1,500

 

Hey I have a 2000 2.7t with 79K am i covered under an emissions warranty? Code P0421

 

You need to get it fixed ASAP. Once you go over 80k, you are no longer covered under the federal warranty.

 

Auditech, man your full of great advice! A real asset to this forum.

All you guys on this cat topic are beginning to worry me though. The 02 3.0 A6 with 120K miles I'm going to buy from a friend has the CEL on. He told me that its been coming on ever since the first owner had the car years ago. He said the 1st owner had the car to the dealership over 10 times in the 5 years he had the car, and they would clear it and then it would come back on. I'm getting 3rd hand info here, but from what my friend says, they never could put their finger on why thecel would come on. I will get the code asap before I buy. (maybe they didn't want to replace that cat under warranty and wanted to wait for the 80K to run out. Who knows.)

Is the VAG-com tool better for reading codes that the audi computer? Was thinking about investing in one to diagnose problems myself?

What I'd like to know is, and if the Fed's are listening I'm only talking hypothetically of course, can I replace the cats with straight pipe or maybe an aftermarket cat?

If need be, a bung could be welded in the straight pipe for the O2 sensor. Not sure if its in the cat or not since I haven't looked under the car yet. My friend owns a muffler shop and could get me a aftermarket way cheaper then 1000.00.

By the way. If anyone does have a cat replaced for whatever cost. Get the old one back. Old cats can be sold for scrap to the right place for big bucks! Like 100.00-200.00+! This is because there is precious metal in them to do the job they do. I think platinum or something. That's the story I got from my muffler shop owner friend. That will help offset the cost of your new cat if someone wants to go through the trouble. If not, then the repair shop will pocket the cash.

 

Greetings everyone. Well, I started this issue and wanted to give an update and ask for some advise. As mentioned, I was receiving CEL Code P0421 & then started receiving P0431 a few weeks later. I finally buckled down and had both the Cats replaced on my car by a local muffler shop. Ken's Mufflers in Dallas, TX. Great guy....been doing work for me for over 10 years and I trust him completely...always a quality job. I must admit, AudiTech79 if you're reading, that they did tell me they would NEVER do another one of these again due to the difficulty in changing these out. He had the car over a week (I wasn't in a rush anyway). They got the original parts replacement, did the repairs, basically put the car back together again (ha) and cleared the code.

And the story continues.....I've been driving for about a month now. No issues. No lights. Finally happy with this second hand purchase. Well, until today! Guess what came back on: CEL0421 & CEL0431. Now that I've had the Cat's replaced, can anyone provide further troubleshooting advise. I'm honestly hoping it's a simple O2 sensor or something. Even after spending the money for this quite expensive repair, I just want the darn thing fixed. As I know weather can sometimes affect a car's performance, the temperature has been swinging 50 degrees (between 20's & 70's the last few weeks here). I do let it run for a minute or more every cold morning just to get the chill off. The light came back on today driving down the freeway at about 60mph in normal traffic. No stopping & starting.

What now??? Thanks in advance.

 

Its a software issue, if you have any engine except the 3.0L then go to the dealer and tell them that you have brand new cats installed but its still throwing a cat efficiency code. They will know what to do.
If it is a 3.0L, well i don't know what to tell you.....

 

Figures....I have the 3.0. I'm just going to put this car on the side of the road and let someone steal it. Appreciate all the advise and expertise. Have a good evening.

 

Mr Auditech, Why won't the dealer know what to do with the 3.0? Its still an audi motor that's been around for years.

I'm looking at buying an 02-04 a6 3.0 an am leaning toward the 3.0 because its non turbo, thinking its less complex to work on and more reliable. I have heard that I won't have to worry about the coils going out and the turbos failing.

Thanks.

PS. Hey Dallas, where you gonna park that car?

 

Well I'll tell ya', honestly the car is a good size and if it weren't for this flippin' light I'd enjoy it. Funny thing is that Audi said they were going to replace the Cats too so that's what I had done. At this point, I don't know if I would even trust the Audi dealership. Best of luck if you buy one. Mine's an 2003 A6 with brand new Cats and it's still having problems. I was inclined to get the O2 sensors replaced next but don't know what to do now.