Prius C "See You..." Screen

If you are referring to the "Trip Summary" screen, you should see both how much it cost, and your MPGs for that trip. Here's an example:

 

I think it's because you put in a comparison car's MPG. The cost screens change from Savings to Cost depending on whether or not you put in that comparison number.

 

I believe this is the case as well. Here are a couple pages from the manual, other than that there's not much reference to it. I would try turning off the fuel comparison and see if that solves your problem.

 

Found a thread about the same issue here.

 

If the Trip Summary screen shows 99.9 MPG, there is a simple math formula to compute the actual MPG of your trip. MPG = trip distance x cost per gal. / cost of trip. The trip distance and cost of trip is found on the Trip Summary screen when you turn the ignition OFF. The cost per gal. Is found on Settings Consumption screen entered during your last fill-up. For example, MPG = 9.2 miles times $3.85 divided by .30 cents = 118.86 MPG. I keep a pocket calculator in the arm rest compartment to do the math. My highest MPG Is 164.06 MPG on a 9.2 mile trip to the movies. The reason for this super MPG is the trip is downhill with a loss of 1028 ft. over the 9.2 mile distance. Returning home uphill the MPG averages 54.6 MPG. There are 5 manual stop signs and 1 green yellow red stop sign enroute. I make this trip often to see movies at the USMC base theater with simular MPG results. Note: altitude data for the trip obtained using the Google Earth App.