Did a search, but I have a few more questions.
2002 A4 1.8T w/ 85000 mi. CEL w/P0420 code. Canged both O2 sensors andCEL returns.
Good driveablity, good power, good mileage and no sulfur smell. So how does a cat go bad on a car thats running well? Will a pressure gauge in the before port show more than a couple of pounds due to restriction? I just want to make sure it's the cat.
I checked with Audi and they cover the cat only up to 80,000 mi.
I believe it's a CA car now in NH. Will an aftermarket cat solve the problem or will only OE work?
And lastly, with such a price difference between non-OE cats ($250-$450), is any one better than another?

 

Its the cat converter, changing the O2 sensors won't help.
You can get a universal cat converter and have it welded in if you wanna save some money.