Not sure how much his applies- I have a 2009 A6 Avant with the 3.0T supercharged V6 motor, that recurrently gives me a check engine light and a p-40411 code. My indy shop told me its essentialy a carbon buildup issue that blocks the SAI system from flowing enough air. The SAI (Secondary Air Injection) system pumps air into the exhaust to re-ignite any unburned fuel, sinceall the air was used in the power cycle). They told me 1) it has ZERO impact on reliability or gas mileage, it simply means the car pollutes a TINY bit more, and 2) it was a HUGE amount of labor (est. $3-4K) to get at it to fix it. Since Ohio is no longer an inspection state, they suggested I ignore it. I've run the car for at least 4 years since then with zero issues, every few months the CEL pops up and I delete the code. Hope this helps.