I always use the "old fashion" method. Current mileage, filler up, drive, current mileage, filler up.. walla.. Subtract current mileage from previous written mileage = divided by gallons pumped = MPG... simple accurate and the TRUE mileage you got on that
tank of gas..
The DIC only give the average since the last time the battery was disconnect, or the ECM was reset.. Over time and its use is what you get with that.. so that number goes up/down consistently.. If mainly hwy driving mileage MPG goes up, if only city driving mileage goes down...AND those numbers are averages
, not very accurate as far as what you are getting right now..
Calculating Your Car's Miles Per Gallon (MPG)
1. Fill up your car's gas tank all the way.
2. If your car has a trip odometer, reset it, or record the master odometer mileage.
3. Drive your car as you normally would, and let your gas tank deplete to at least a half of a tank of gas.
4. Get to the gas station and fill your tank again.
5. Record the amount of gas it took to refill the tank.
6. Record the elapsed trip miles or new odometer mileage.
Get the miles traveled from the trip odometer, or subtract the original odometer reading from the new one.
Divide the miles traveled by the amount of gallons it took to refill the tank. The result will be your car's average Miles Per Gallon yield for that driving period.
e.g. 312miles ÷ 16gallons = 19.5mpg
You can repeat this procedure every time you refill your tank to continue to monitor, and attempt to improve, your gas mileage.