2000_A6_2.8_Avant

For the past three years I have been dealing with a persistent insufficient airflow with the secondary air injection system (P1411 & P1423). Long sotry short, even the Audi stealer ended up scratching its head about why I kept getting the codes (both combi valves replaced, etc., etc.). I figured I would just have to live with clearing the codes once or twice a week.

Two weeks ago I get a couple of new codes (yipee!)-P1122, P1140, & P0160. Basically the 02 sensor on bank 2 at the cat is kaput. So I decide to replace both 02 sensors on bank 2 just to be somewhat consistent.

Went almost a whole week with no codes (not even my P1411 & P1423). Today I get a P0421 code. This is telling me "Warm up catylist below efficiency" bank 1.

It just seems too coincidental that after I replace both bank 2 02 sensors, all of a sudden the cat on bank 1 is going bad.

Is is just bank 1 02 senosrs are not as fast and efficient as bank 2 02 sensors and the ecu is jealous, or could it really be a bad cat??

And why did my P1411 & P1423 codes go away?