Hi again!
My son's 99 A6 (218k) keeps throwing 0432/0422 codes. First time I cleared the codes was in Feb. Just came back today. His car seams to run fine, it does sound louder than mine. So the ? is- is he due for cats or could it be the secondary 02 sensors ?

Thank you.

 

Anybody?

 

Quick answer to your ? -> YES
It could be your o2s or cats. However usually when you get the cat codes it won't be the sensors, since there are separate error codes for O2 and cat itself. Considering you have way over 200k miles, I'd say there is a good chance the cats are toast.

Mine started throwing codes at 130k and 11 years of age - so I cut them out. I don't know if your state does emission testing or not but I would take that under consideration since you are looking at 1k per side (dealership price / indy would be cheaper).

 

My state doesn't do testing. My son would be more likely to do a bypass than replace the cats. I'm not sure if the universal cats will work on the A6. Can get for around $70 a side, (some assembly required) BTW what is the OD of the pipes?

 

I heard some people had luck with aftermarket cats while others still had the car throwing codes. It's basically gambling. I'd rather cut them out, free up some power and foul the sensors into believing you have a working cat.

I'm not sure about the OD of the pipe - sorry. I had a friend with welding / cutting / stretching pipe equipment help me out and he made everything fit.

 

Here's an update. Got underneath my son's car, and someone had beat me to gutting the cats. Cut one off and pull it out, and it was all cleaned out inside. My question, and thought is that the rear O2 sensors must be bad? Is this true?

 

Not necessarily. The tricky part with fooling those sensors is that they can still throw codes intermittently (like every 500 to 1000 miles). Many people who take out the cats have these problems some very frequent (like every 20 to 100 miles) and others do a better job of installing the fouler and it keeps the sensors from reporting anything wrong for 1k miles.
You could try replacing the O2s of course first (only rear affect these codes) and you can try to install like a mini cats (O2 Simulator, mini catalytic Converter cel fix) - however no solution can guarantee a 100% check engine light free experience. You might get lucky or you might still throw codes.

Good luck.