I have a 2004 Prius and have experienced a similar problem with the fuel gauge. While the reading is inaccurate when the tank is over half full, the accuracy improves at half a tank or lower. A friend of mine has the 2001 model and complained to me more than once about the fuel gauge on his Prius. Apparently there is bladder liner in the fuel tank that he swears it occasionally will partially collapse, causing a problem with his fuel tank readings, making them artificially high.
After one particular fill up, the reading on my 2004 became totally inaccurate and I brought it to the dealer. The suggested remedy was a new meter computer and filler pipe. The cost? $1150!
Remembering my friend's problem with his car, I decided to "wait and see" if the problem persisted. It is now operating normally without having done the replacement suggested by the dealer.
While your fuel gauge reading is annoying, you can always verify the fuel reading by checking the readings on the consumption screen. At fill ups I've checked the average MPG's against the computer reading and always have been within 3% of the computer reading. By checking the MPG rate and the miles travelled since the last fill up, you can easily verify the fuel gauge reading.
I just rented a Prius from Hertz, they should have told me about the fuel gauge problem. The owner manuals of this car states that you have 2 to 3 gallons of gas, when the fuel light start blinking, well I got 10 miles of warning and have to call AAA to bring me gas. For 21K car this is ridiculous, and they should recall all the models with this problem.
I also did not like the Digital dashboard (pretty hard to read on a sunny day) and the control touch screen I think is not needed, and I would like more to have standard control for the AC and Heating.
I did like how roomy it is when you fold the back seats... I will suggest to rent it for few days to try it before you buy it, I will recommend it for people that do not care about the acceleration, since the car does not accelerate as fast as most of the cars. I think they still need to refine the technology, but it's getting there.
I have a 2004 Pius that is experiencing an inaccurate fuel gage. My local service station where I get the car serviced for oil and filters has a set of bulletins that have been issued. He printed out a bulletin from Toyota regarding certain VIN numbers and indicating a replacement of the fuel computer and the filler pipe. My VIN was not on the list but I am going to take the matter up with my local dealer.
Have you thought of using your trip odometer as a fuel gauge? You must have an idea of your mileage. Simply reset the trip odometer and use it as a backup or even a primary gauge of your fuel supply.
In all/most cars, fuel gauges are notoriously inaccurate. Note: they are in private plane, too!
Also, have you ever considered simply filling up when you are 1/2 full and not worrying about it?
Lastly, go back to my first suggestion!! Use your trip odometer.