I have a 2002 Audi Allroad 2.7T and my check engine light keeps returning with the codes P0491 and P0492.

I cleared the MIL and when I was checking for vacuum leaks last week, I noticed that my SAI system worked fine at initial startup. I heard the air pump running and the check engine light did NOT come on at this time. However, about 5 minutes after the initial SAI cycle stopped, the air pump turned on again for about 10 seconds. THIS is when the MIL / check engine light came on.

I cleared the MIL and codes. This week while I was filling my tires with air, I heard the SAI air pump fire up 5 or 10 minutes after initial startup. I ran to the dashboard and saw the check engine light flash on!

It seems like the MIL light comes on only when the SAI air pump fires up the second time. I thought the SAI system fires up ONLY at initial startup. Are there situation when SAI system turns on again after the car has been running for 10 minutes? Could there be some other ECU malfunction? Perhaps when the system fires up the second time, the air pump runs but the combi-valves are not getting vacuum and opening?

Thanks in advance for any help!!

 

Check to make sure that the hose leading from the pump to the kombi valves do not have any leaks. This is pretty common, especially for a 2002 where the black hose connecting the pump to the valves becomes brittle and cracks and breaks easily when moved slightly.

 

Check your vacuum pods on the front of the engine, after doing much work, I discovered one of mine were cracked. I used some black silicone to seal it up, and everything works great now

 

Thanks for all the replies.

Coltank, what type of silicone did you use? Tub and tile? Fish tank sealant?