How does the c-max compute the fuel used? I reset trip odometer each time I buy gas. When I refuel, I check the display readout. It tells how many gallons of gas used but when I fill the tank it always takes more gas than the display says by around a gallon or so. Is there a fuel line meter for gas usage? Can this be fixed? As a result, the display mpg calculation is always about 2 mpg higher than actual mpg.