Went to mechanic--the code P0442 he says he pulled the code for a bad cat. Any ideas. Can I
 

get an after market one maybe a more performance one and have my mechanic put it in?? My car is over the 8/80 warranty so I am knid of stuck here. I am aware this can be a costly repair.
TIA

The code for a bad cat is just a code. You need to get to the root of the problem before...
 

...spending any money. First off, what engine and model year?

It is a 2000 A6 4.2. I replaced the O2 sensor 8-4-2007917819 bank 2 secondary air injection)

Ugh. OEM O2 sensor? You're probably looking at a cat then. :-(

That is what he told me.I am going to pick-up the car tomorrow and weigh my options.I can drive...
 

the car the way it is ---- no loss of power or rattling noise.

Sorry, but I had to fvcking LOL : ) What are the chances that two green 4.2's
 

would suddenly have bad cats? And amusingly enough, I received my emissions notice today :P

My dads old 4.2 had a bad cat code from 2003 until it commited suicide in 2007. I really wouldn't wo
 

rry about it.

Thanks.I think I am going to get two magnaflow cats and put them on.

How did it pass emissions?

BAD CAT from P0442 code only??? No way!!!
 

P0442 code is a small evap leak, like a gas cap, vacuum line etc. Did you have any other codes like P0420? If not, run away as fast as you can from that mechanic.