After filling my car, a 2009 Hyundai Santa Fee, which was 3/4 full to begin with, the gas gauge immediately fell below empty and the empty warning light came on when I started my car. The mileage remaining was flashing as no miles left. I pulled over a few minutes later, and took the gas cap off, and put it on again. I have no idea if this helps, but I do it routinely, as this happens ALL THE TIME! As I drive, randomly the check engine comes on and off after filling with gas. After driving for awhile, the gas gauge goes up, but never to full. As time has passed (about 5 weeks) it is getting more and more erratic. Now it will go down to empty when I do not fill the tank. Just randomly. And I find that I never trust how much gas is in the car. I write down the mileage when I fill up and keep track. I worry that the computer is going crazy and will not register that the car even has gas in it. I feel very strongly that this is a hazard, as I could run out of gas, and that Hyundai should issue a recall as this is very obviously a VERY COMMON PROBLEM.