This was something that was wrong with the car when I bought it and my mechanic fixed it for free, but explained to me that the price to fix this normally was around $600. In the gas tank filler there is a valve that releases air out of the tank. A bug crawled in there and caused the valve not to work. When the valve doesn't work, the car runs a code, preventing it from being inspected. My mechanic had to drop the entire fuel system, empty it and run a smoke machine on it. Find out where the problem was, clean it out/replace the part. Return the fuel system to the bottom of the car.