| First i would use the old fashion way to determine fuel consumption. Prior to high tech we used to fill up the tank to the rim. reset the trip odometer to 0; drive for say 100 KM (in your case) then fill it up again to the rim. How many litres? devided by your KMs. Allow a little room for errors as you may be off on how you fill up the car in both cases. Try to do it in the same gas station/same position/car tilting etc.
To be sure and for comparison purpose disconnect the (-) on battery to reset electronics (you may need radio code) do the same through the computer then compare both outcomes.
good luck
billb | 
