From all the old threads on the forum the P0422 indicates a a bad cat converter but I replaced the cat about 10,000 miles ago. Could the cat really be bad after only 10,000 miles. Could the rear O2 sensor be bad and this code goes off. The car is a 98 A4 1.8t.

 

i have been told that p0422 means bad cat...but i was living with that code for a few weeks and i did the non fouler on the rear 02 and it fixed it so try giving that a try