We took our 2008 Prius in for a check engine light. The dealership said oxygen sensor was faulty. Changed that and had them change the serpentine belt while there due to cracks in the belt. My wife filled up the car the next day ( it took 13 gallons) but gas gauge was not registering a full tank. We drove 67 miles and I decided to pull in to a gas station and see how much it would take since the gas gauge was not working properly. It took over 7 gallons. What in the world is going on? I cannot see any fuel on the ground nor smell any gas.