2 weeks ago, while I was driving my 05 A6, the check engine lights came on. I went to this guy that diagnosed the problem for me. The code was P2404. It was apparently related with the Evap system. The guy turned the lights off for me and told me to see the dealership if it turned back on.

Last Monday, the lights came back on again. I drove it to the dealership and had them checked it out. The dealership said that it was an unusual problem. They told me there are two possible causes. 1st was the EVAP program needs to be updated. 2nd was the detection pump was faulty. However, when they tested the detection pump, it passed and no need to replace it. So they just cleaned up my gas cap and checked for any leaks along with the EVAP system. I end up paying $200 that day.

However, the lights came back on couple mins ago. Can some one help me figure out what is really wrong with my car? I am sick and tired of that check engine lights turning back on and on again. This is the 3rd time it came back. Can someone help me figure it out??

 

I read a post awhile back (think it's a sticky at the top of the A6 forum) about fuel faults on these cars and it involved the smell if fuel due to a broken fitting on top of the tank. Take a look and see if that is related to your issue. The author of the post was auditech79.