Hello. Just bought an A4 quattro 1.8. The check engine light came on and code read P0422. I changed the pre-cat 02 sensor a week ago and erased the code. It just came back on yesterday with the same code. Could this be the post-cat sensor needs replacing as well? Is the cat bad? What is the most common repair? Any help would be appreciated. Also, car has aftermarket intercooler and cold air intake which i intend to replace with stock parts.