I would give it a shot. However, my car isn't here right now.
For those that would like to try it, I found this from Google search. Seems like you need to use Test 19 to unlock the tests, then enter into Test 20 and then change the correction factor.
From what I understand, it is correction factor based. So, X.XX (One . Tenths Hundredths). Similar to that of a dyno.
So go fill up your gas tanks at the gas station. Reset the OBC's MPG readout on the instrument cluster and the odometer mileage. Drive around the way you usually do until you have consumed about 50-75% of your gas tank. Go back to the gas station and refill your gas tank. Then it is a two step process.
1) Read out what the OBC says the MPG is.
2) Manually calculate what your MPG from the odometer mileage divide by the amount of gas you put in your car.
You will find that the MPG you calculate will be lower than what the OBC says. I am assuming that the correction factor is percentage based.
Correction Factor = 1 - [(OBC Readout - Calculated MPG)/Calculated MPG]
Can anyone confirm this hypothesis? My car isn't with me at the current moment. Thanks.