I think the fuel sensor on my 2005 malibu is bad.

To fix this, you have to drop the gas tank to access it. You will want to run it low on gas so it's not as heavy to deal with. Then depressurize the fuel system by removing the fuel pump relay, and starting the car. It should run for a second and die. Take the straps loose that hold the tank up, and lower it enough that you can access the filler neck and overflow hoses to take them off. Lower the tank enough that you can disconnect the fuel lines and the connectors for the fuel level and fuel pump. You should then be able to pull the tank out. If your car has around 100,000 miles, or more, you may want to replace the pump at this point while you're at it. If you get a new pump, it comes with a new sender as well, and since you're doing the same thing for both, it makes one less trip into the tank. You will have to remove the locking ring, which requires a punch and a hammer to remove. The pump and sender will then lift out. You can then remove the sender from the pump at this point, and put everything back together. You will probably want to empty any remaining gas into gas cans so it's not as heavy going back up.

New gas cap