T-Roy

I have a 2003 A4 3.0L with Cat issues.
I scanned and got codes... P0421, and P0431. Both to due with: Warm-Up Catalyst Below Threshold (Bank 1 & 2).

From what I've heard and read, this job is a PITA, and so it's also not cheap to get a shop to do.... Any experienced 3.0L owners out there that took care of this?
Are the cats and down pipe one piece? Are they separate from the headers?

(yes, I've used the search function.. didn't find my answer.. hoping there is more development on this subject now).

Adam Stasiak

This will surprise you. The problem is with your wheel balancing, CV joints, or lower and upper suspension links. The car shakes and this causes the O2 sensors to disconnect from the wires.
So the problem is not with the cats or sensors, but with the shaking of the car during acceleration.

T-Roy

Interesting thought... but I'm not convinced that this is the case with my car. The wires at the O2 sensors seem to be in contact. I guess its possible that the wires have shaken lose somewhere not visible.

I will take a thorough look I get some time. However if it is my Cats.. any suggestions?

Aftermarket cats, universal cats, are the cats and exhaust manifold one piece?

Thank you,
Trevor

Adam Stasiak

It is impossible that you get 2 cats faulty at once, unless you fueled at Shell or you buy gas at some funky gas station and the gas does not burn 100% so you get sediment inside your cats and they don't work properly. Try switching to clean gas like Petro Can, Esso, Exxon and add good fuel injector cleaner to it for 4 weeks or so to let the inside of your cats clean themselves.
The cats on AUDIS are good quality, except if you really speed all the time they shrink and eventually their diameter becomes close to half an inch, but this would not give you fault codes. So I stay with vibrations or bad fuel as the reason for your fault codes. Don't waste your money to replace your cats.

T-Roy

I only fuel at Petro, rarely Esso. So I doubt its the gas. Thanks for the tips. I guess 'll get some good injector cleaner to be sure, and i'll start following sensor wires.

Thanks again.

Adam Stasiak

I had the same codes and the problem was with my spark plugs, as I decided to test E3s and the fuel was not burning completely. Changed to Bosh Platinum and the problem stopped.