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: 64,672 mi (47,000 mi - 83,000 mi)
Visitor, 2009 Toyota Prius, 80,000 mi
ran the battery low , then the gas guage registered 1 blinking light, filled the tank and it registered a half tank ..6 bars and stays that way 100 miles burned.
Visitor, 2007 Toyota Prius, 83,000 mi
Fuel gauge reads about half full when it is filled completely.
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.