I have a 2009 Prius. Yesterday, I had a very strange (to me) thing happen. My gas gauge read all notches, full. As expected, it went down a notch at about 120 miles. I sat in a parking lot for a bit with the car in ready, running, and park. I noticed that whenever the car would switch to using gas, the gas gauge would change. It would suddenly show all notches again, instead of missing one. When it would switch back to battery, the notch would move down again. It eventually moved down 2 notches (which is probably accurate since I was sitting for about 30 minutes) and then would jump back up to full when it switched to gas again. I didn't notice it doing this when actually driving the vehicle, just when sitting in park with the car running. Anyone else experience this? Is this something I need to be concerned about?