This just started a few weeks ago and it happens randomly.
Here is the issue when I'm driving all of a suuden I hear a tone and on my dash it states that my gas tank is open, when it's not then the Check Engine light comes on. I've tried tighting the cap etc... still nothing....
You probably lost the pressure in the fuel tank. Have you read the code?
One easy way (at least for now) is to flip the rubber in your gas cap around. I doubt it'd help much but it's worth a try. Again, try reading the code first.