hello. this is my first post. any suggestions would be great. my parents have an S70. almost every time they fill the gas tank, the check engine light comes on. i know the gas cap is on tight as it's happened to me as well. they take the car to their mechanic, and the codes say faulty gas cap. the mechanic has replaced the gas cap at least 15 times. is there something else in the fuel system that can be causing this?

 

I think I posted a similar problem a while back. Had been fighting the light for a year, My Volvo mechanic dropped the tank (or so he says) and located a crack in a vacuum line. Not sure what line he was talikin about but the problem is finally fixed.