DTC codes P0421/P0431, needs new cats!
 

Dealer is giving me the run around about paying for the repairs on the car I bought from them 2 days ago which was guaranteed to pass emissions. Drove my new-to-me 2002 A4 Avant 3.0L Quattro 6spd w/ Sport Package with every available option(!!) for 2 miles to a gas station before i got a CEL. Codes read that I need new cats. I can't register the car until it passes emissions and temp tags are counting down. Anyone know a quick fix to squeak through emissions until I have to get under the car and replace the cats? I've heard Sea-Foam spray through vacuum lines, in the fuel, straight into the throttle body, etc. Anyone had luck? Right now I'm sitting on a very expensive, 3500lb paperweight. Any help would be great!!

how many miles are on the car?

seafoam will not help with the codes for the cat... also you cannot clear the code and expect it to pass. it will fail if you try to have the emissions done immediately after clearing codes and or removing the battery. you must drive it around for a period of time to get the readiness modules set.

a quick fix to get it to pass(note this: i do not take responsibility for anything of what occurs from what you may take from this information)

get another 2 extra O2 sensors for your car. locate the plugs where the SECONDARY O2 SENSORS PLUG IN.(the sensors are located after the cat. plug in the new O2 sensors that you acquired and zip tie the sensor somewhere that it will not be seen or touch anything. <- the sensor will get quite hot due to heating element.

what this does is make the ECU think the cats are indeed fine because the O2 sensors (primary and secondary[before and after cat]) are reading different values. so the ecu thinks the cat is fine. if primary and secondary O2 sensors send the same or close to same value, the ecu thinks that the cat is bad.

now granted the cel codes you got could also mean the O2 sensor is bad. so you could just try replace it..

another thing to try is get 18mm spark plug defouler and install that with the secondary O2 sensor. <- this brings the sensor out of the exhaust stream.

and if you do any of the above, do not tell the emissions station that you did it. they will fail the car.
the dealer you got the car from wont fix this issue for you?

It's at 110K and came from an Audi specialist dealership, so I'm assuming they flashed the ECU and said good enough, it's his problem now. I'm still negotiating with the dealer about fixing the vehicle which they guaranteed would pass emissions in NC. I can honestly replace both cats and O2 sensors all around without a great deal of difficulty, it's just the principle of the matter. The O2 sensors are a good idea, I will try that. Even if that doesn't fix it, I'm sure at this mileage they'll need to be replaced soon enough anyway. The car is going in for a full mechanical inspection and we will see what happens. Thanks for the help!

I forgot to ask, can you recommend a particular brand of non-foulers to use? I'm coming across so many I don't know where to start. Thanks!