Today, I went to a Gas Station in the city. After having the attendent fill the gas, I proceeded on. However, after an hour, the Check Engine Light came up and the Emissions Workshop signal popped up. I was like, ahhh man, not again (I just had the vacuum hoses changed a while back after getting the same message). I went to my local mechanic who was kind of enough to run the code for me. The code was P0455. It stated " Emissions Control System Leak Large". I explained to him that I just had the vacuum hoses repaired about a month back. He told me to check the gas cap. Walaaaaa! The gas cap was loose. The damn gas station attendent didnt even bother to close it. I closed the cap and turned the car off for a few minutes. When I turned it back on, the CEL dissapeared. Does this mean that the code has been cleared too, or will it still remain in the memory until I clear out the codes? My mechanic said he would charge $35 bucks to clear the code. I just don't want the code to linger in the memory, and then if I have a problem in the future, this code along with the new code will come up. Is this code automatically cleared do the CEL going away after I tightened the gas cap?