Just bought a 2004 S4 a couple of weeks ago, 46,000-ish miles. The first cold morning, before the car was completely warmed up I got a check engine light. Read the codes and got P0491 & P0492 which says Secondary Air System Bank 1 & 2.
Cleared the codes, and drove for several days without any issues. Then last night I took a drive, about 15miles or so, and after the temp gauge was to the normal range, I got a check engine light again. Again the same two codes.
I have done some searching, but have not really found all the info about this system. I know it injects fresh air into the exhaust so that the cats get to optimal working condition sooner. But I was surprised to get the fault after the car seemed to be warmed up, does anyone know when and for how long this system is active? Any quick checks, or known problem areas?