Average MPG on trip computer

[repenttokyo]

it's an average of your last x hundred miles of driving.

[ahlem]

If I rely on the trip computer I get 15.7 MPG. If I do the real math I get 22.1 MPG. I do have a 3.9x diff. Is there a calibration issue?

[Russell]

mine was accurate with in 1/2 mpg the last time I checked it with actual consumption.

[Russell]

If you mean it resets every xxx miles, I think you are wrong. It is only reset when you reset with the S/R button.

[repenttokyo]

If you mean it resets every xxx miles, I think you are wrong. It is only reset when you reset with the S/R button.

that's not what I mean. What I mean is that your car looks at the last X hundred miles of driving and presents the average over that time. If you hit the reset button, it starts it's count for the average period again. I seriously doubt that the car remembers the entire fuel consumption and mileage between resets, it is most likely only looking at a specific time period within the reset window. that is how these systems usually work.

[BMWCCA1]

No reason for it to be off unless some messed with it, or replaced it, but you can recalibrate it. Search this site for "obc hidden features" or take a look here: http://home.iae.nl/users/bts/obc.htm

[Black 535i]

...I believe that the onboard computer figures out averages and you are figuring out the 'actual' average as I do. I too am way off the onboard computer averages everytime. It takes into account how you drive, how you accellerate and all that whereas we just figure out the average of mileage divided by gallons used and not how they are used. Anyone else have a theory on this?

[billy]

if you select mpg on the OBC, you should notice that the average will reset every time you press s/r button, therefore you would just start getting the mpg average from now onwards rather as say the last 100 miles

[uscharalph]

that's not what I mean. What I mean is that your car looks at the last X hundred miles of driving and presents the average over that time. If you hit the reset button, it starts it's count for the average period again. I seriously doubt that the car remembers the entire fuel consumption and mileage between resets, it is most likely only looking at a specific time period within the reset window. that is how these systems usually work.

It does calculate based on miles driven since reset.

[uscharalph]

The one calculation the obc does make based on a time frame is RANGE. It calculates fuel on hand by mpg over the last 20 miles driven.