Warm-Up Catalyst Below Threshold (PO421/31)

[Spotty]

Hello Everyone - Just joined this forum as it's my last hope to get creditable input regarding yet-another problem that's developed with my 2002 A4 Quattro 3.0L MT6. I'm handy with a wrench, so this is the last in a string of problems that I've been unable to solve. Here is my question. For years now my car throws the following "Check-Engine Codes, P0421 & PO431. Both are associated with the Warm-Up Catalyst Below Threshold (Bank 1 & 2). I took the car to several mechanics, including Audi, and all claim that the converters are shot and should be replaced. As we all know, this is expensive and as I already have 120K miles on the car the repair would be 50% of the remaining value of this vehicle. So, I started with simply replacing the Primary Oxygen Sensor (Before Converter), as a mechanic used a tool to identify which Sensor is failing. These were replaced with BOSCH (very pricy) OS and this did not fix the problem. I also attempted to purchase used CC's from a wreaked car and the law prohibits junk yards from selling them without certification. So, the light comes on much more frequently now. Strangely enough, it seems atmospheric as the light trips frequently in one location where the weather may be a bit cooler? As an interim fix, I purchased a code-eraser and simply turn it off. However, with yearly Emission testing, the car needs to drive over 100 miles before they will approve the car for the next year. This is becoming more difficult due to the frequency. Regardless, can't sell the car to a private buyer as I wish to be honest about the lingering problems. I'll likely be unable to pass Emissions and I can't see spending over $2K to fix yet another problem with my first Audi. Is there a cost-effective solution??? If anyone has interest, I'll happily list the MANY other problems affiliated with this car. Thankfully, it's running OK......today! Thanks for your help.

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[Dan1969]

hmm, you should have replaced the after converter sensor, that has worked in the past. If the problem persisted after replacing those, then is time for the converters themselves.

[auditech79]

Chances are the cat converters are still working good enough to actually past emmissions, but the engine management is too sensitive. You can do a couple of things,

1. Find a company that can make a custom chip that will delete the function of the after cat O2 sensors eliminating the check engine light. Not legal but not detectable either.

2. Install a set of spark plug non foulers as a spacer between the O2 sensors and the cats. This is cheap and easy, but is only a temporary fix. 1.8T guys do this all the time when running a test pipe (no cat) to get rid of the CEL, however it usually only works for 500 miles or so. The other problem is the emmissions tech can see it, so if he isn't a pimple faced moron, he will fail you.

[rayveedub]

the 3.0 cats are a real common problem, you need to replace them. However if you want a easy way out look at these,

http://www.raimotorsport.com/RAI-J-P...p/11620vib.htm

this will trick the secondary o2 sensor into thinking everything is okay. Ive been using them on my 3.0 for years now. oh yeah "off road use only"

[Spotty]

Sorry to see that I'm not alone with this problem. However, I'll start with the J-Pipes, then new After Cat. O2 Sensors. If that doesn't solve it, then it's off to the junk heap.

[rayveedub]

j pipes will work, we use them in many applications.

[sonny67]

Spotty- Was wondering what you ended up doing? I have an 01' Allroad 2.7T 93k that is throwing the same codes. Replacing the cats with aftermarket direct fits will be $700 but would rather not spend the cash.
Thanks!
Sonny

[TheGabe]

Would love to get some help? I've been browsing the forum like crazy today trying to find some answers.

I have an 02 a4 3.0 6 speed and i am getting this code and have been getting it for awhile now. Anyways i just cleared it at my local autozone. I have emission testing this month and am hoping i can slide by the test here in Utah, but i'm highly doubtful. I don't really have the funds to drop a few grand on replacing the cc.

Sounds like it's a very common problem with this model. Anybody have any advice/tips/ experience with how to get by emissions with this code. As for now my CEL is off but if i take it to get tested the shop will probably tell me i need to go through a drive cycle so that the codes can reset fully(which inevitably means the CEL will come on again)

I was sold this car with the CEL on from a dealer...This car should have never passed emissions when i got it 2 years ago (dealers required to get car tested/registered before selling). They told me the CEL light was not a big deal...well the dealer screwed me over in more than one way.(LONG STORY) They went out of business shortly after i got my car.

Just wanted to share my problem/experience. Love my car but this problem might make me hate it. This is my first post. Nice to be part of the Audi community.

[Spotty]

I still have the problem as I vowed not to invest one more dollar into further repairs. I've simply turned-off the code and have escaped yet another year with emission testing. However, this may become more difficult.

As for the previous post from "TheGabe", I would agree; you got screwed. I've never heard of a dealer selling a car with such a problem. They clearly knew this would be an expensive repair and chose to unload it on the next victim. I assume that they got the car in trade and during their ownership the light came on. Hence, they were stuck.

I was pleased to see that Audi replaced (under warrantee) the faulty Coils. Although, they needed a pending class-action lawsuit to force this issue. From my research, the P0421/431 issue is well known and documented. Per the dealer, this is tied to faulty Catalytic Converters which are extremely expensive to replace as they require the full exhaust. Like several other costly repairs, my CEL codes started around 80K miles. As the car still runs fine, gets good mileage, I've chose to live with it.

I did research the "J-Pipes" discussed earlier in the thread and may be the most creditable solution. For $30/pipe, and straight-forward installation, this may be your only option. Otherwise, O2 sensors (all 4) could lead to a solution, however I doubt mine were really bad.

Hope this helps. I would love to buy another Audi, however my 2002 experience leaves me questioning their Quality and Reliability. My pockets aren't deep enough to go that route again.

Best of luck!
Spotty