Fuel Gauge not going down?

This is normal. When you overfilled the tank, that resulted in 1-2 gallons of extra fuel being added above the point where the gas pump normally would shut off. I would guess that you will start to see the fuel gauge bars decline from 10 to 9 after another 100 miles or less.

 

Yep, it's possible that you'll see up to 200 miles before the first pip drops. But don't worry it will happen!

 

I once took a trip in my Prius and thought the same thing! I filled up before leaving and drove 185 miles (almost to my destination) and the fuel gauge still registered full! I immediately thought something was wrong with my gauge. At 186 miles the gauge registered 1 pip below full! What an amazing vehicle!

 

Found this PDF for MALFUNCTION IN FUEL RECEIVER GAUGE - for future reference.

 

Seriously, about one person a month comes here and thinking that their fuel gauge is broken just because they managed to get that extra couple of gallons in there and it takes a while for the top pip to drop.

I don't have the tank bladder here, so I manage to get 12 gallons in there every fill. So the top pip is equivalent to 3 regular pips for me every time.

 

Care to elaborate how you don't have a tank bladder?

 

The tank bladder is only installed in the North American model prius. Australia, UK, Europe and Japan etc don't have them.

 

Didn't know that! Wonder how much trouble it would be to get one and install it...

 

Depends upon if you care that your check engine light will remain permanently on if you disconnect the emissions equipment associated with the North American fuel tank.

 

Do we know what code is thrown?

 

In the summer it takes about 150 miles for my gas gauge to drop from completely full so give it a while longer before worrying.

 

Well, it would probably be one or more of the following: P0441, P0442, P0446, P0451, P0452, P0453, P0455, P0456. These relate to problems with the Evaporative Emission Control System Incorrect Purge Flow or Vent Control Circuit, Evaporative Emission Control System Leak Detected, and Evaporative Emission Control System Pressure Sensor/Switch.

If you care to learn more, I suggest you subscribe to techinfo.toyota.com so that you can access the repair manual info, see the complexity of the North America 2G Prius fuel tank (and recognize the engine ECU has the ability to monitor the fuel tank sensor monitoring the vapor space between the flexible bladder and the tank exterior shell) and consider what will happen if another tank lacking the bladder and sensor is substituted in its place.

 

I don't know how large the bladder is but the tank is 11.9 gals.

 

What is your tank mileage according to the MFD? You could use that to guesstimate how much gas you've used to keep from running dry.