The fuel gauge may read incorrectly. A service bulletin has been released by Toyota regarding this concern. The fuel filler pipe or the instrument cluster may need to be replaced to correct this concern.Google+
Car Problem Reports
Toyota Prius Fuel Guage may not read correctly
Toyota Prius Problem
Average Mileage: 96,714 mi (23,000 mi - 171,000 mi)
Visitor, 2009 Toyota Prius, 79,000 mi
Fuel gauge indicates tank is near empty but it takes less than 7 gallons to completely refill it. Consistent with this, the gauge seems to go down more quickly than fuel economy would suggest.
Visitor, 2005 Toyota Prius, 114,500 mi
The fuel gauge is stuck at the 6 th notch and it doesn't move after filling it up to the full tank.
It's scarily driving when I don't know how much gas I have left.
Visitor, 2008 Toyota Prius, 47,000 mi
gas tank is full but gas gauge only registers half a tank, recalibrated system and still registers half tank.
Visitor, 2004 Toyota Prius
I found out that the fuel gauge will not move unless you fill up the tank at around 60000 miles. My Prius now is 102000 miles, the fuel gauge is getting worse. The fuel gauge was at the last light and flashing, but it only take 7 gallons of gas to fill it up. Now, the gauge goes down one light after 30 miles drive, and the 3rd light at around 70 miles.
Fuel gauge is not reading correct
Visitor, 2007 Toyota Prius, 171,000 mi
The fuel gauge is not correctly responding to fuel consumption after filling fuel tank to full. It continues to register as full even after driving 100 miles.
Visitor, 2010 Toyota Prius, 79,100 mi
The fuel gauge shows three bars, but the miles to empty is showing 10.
Visitor, 2006 Toyota Prius, 135,000 mi
Fuel gauge is stuck at one bar past half. I've filled it to full twice but it doesn't budge. I've driven it 300+ miles, but the gauge doesn't move up or down. I'll not fill it over the weekend to see I it'll go down.
Visitor, 2005 Toyota Prius, 150,000 mi
I put gas in the car. Still shows one bar.
Visitor, 2009 Toyota Prius, 107,000 mi
Not fixed, stuck on one bar, but filled car up and no change...