I've had my car for 2 weeks. It kept throwing p0402 codes. This weekend we replaced the pre-cat o2 sensor (and found that the o2 sensor was a 5 wire sensor, instead of the 4 wire sensor that all the parts stores said it was).

While replacing the o2 sensor, I noticed a small hole in the weld by the o2 sensor. My mechanic thought that it was an imperfection in the weld - but still a good weld. I thought it looked like a real hole - but I didn't try to test it. (not sure how to test it - maybe by sticking a piece of wire into it.)

After a few medium trips (5-10 miles), the CEL comes back on.

This time the code is a p0422 (cat less than efficient - or something similar).

By the way - the tester that I've been using is a 'standard' odb2 tester. It's just dawned on me that maybe the meaning of a p0422 code is different on some cars than it is on a VW/Audi?

Thanks for the input

PS - I posted something similar the other day, but used the wrong error code. I had just read about some other code, and used that code throughout my post. To much reading and not enough sleeping. Thanks!