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"Average" in the MFD - What exactly does it mean?

Discussion in 'Gen 2 Prius Main Forum' started by pnerd, Feb 14, 2009.

  1. pnerd

    pnerd Junior Member

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    Hi all,
    This is about a 2006 Prius.
    I know there are many similar threads asking this, and I believe most people would say the "Average" is simply total fuel volume consumed divided by total distance traveled since the last time the "reset" button was pressed. Yes?

    [​IMG]

    Does anyone know this definitively?

    I ask because my "Average" seems to respond quicker than I would expect, to recent changes in driving style / traffic conditions.

    I never hit the reset intentionally, but I know it does get hit accidentally occasionally by other people.
     
  2. qbee42

    qbee42 My other car is a boat

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  3. kenoarto

    kenoarto Senior Member

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    It's your rating as a human being ;-)
     
  4. patsparks

    patsparks An Aussie perspective

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    Could it be self explanitary?
    You average consumption over 35 kilometres is 5.1 litres per 100 kilometres.
    As you get more kilometres you will notice the change to your average is slower because each kilometre is a smaller part of the total kilometres traveled since reset.

    Don't over think it, it isn't rocket science.
     
  5. Mike Dimmick

    Mike Dimmick Active Member

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    Simple average of distance divided by fuel consumed, but the amount of fuel consumed is taken from how much fuel the car thinks was injected, not amount pumped from the tank. I recall reading comments somewhere about how the Reset button resets the accumulated error statistics, so I think it's trying to compensate by calculating how much it had to change the air/fuel ratio to get the best burn.

    That may not mean that the fuel injector calibration was off - it may simply mean that the fuel had a different ratio of HC compounds than the fuel that Toyota calibrated it against. That is, more fuel was necessary to burn a certain amount of air than Toyota thought, rather than the injector injecting less fuel than was requested.

    In fact the formulation of the fuel changes with the seasons, as the fuel has to stay within a certain range of volatility while staying at the same octane rating. (The fuel must vaporize to burn effectively, but too much vapour prevents it being pumped from the fuel tank.)
     
  6. pnerd

    pnerd Junior Member

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    Sure, and maybe it isn't.
    No, probably not in my case, because the "35 km" started counting not from a RESET-press but from an auto-reset when it detected a fill-up.

    Correct me if I am wrong, it seems to me that a post-fill-up auto reset does NOT simply zero out the cummulative distance and consumption figures used for the "Average".

    Only if the RESET button is pressed, then you would see the "Average" changing wildly before settling down.
    Yes, the above is what I expect to see.
    Suit yourself.
    But there's usually more than meets the eye: assumptions, limitations, tweaks to the math, differences between model-years.
     
  7. patsparks

    patsparks An Aussie perspective

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    Reset is reset.
    Once the display is reset the kilometres and the consumption are reset, at least that is the case in my car. My car resets every time I fill up, and there is a reset button I can press (or anyone else in reach) to reset the whole deal to start from scratch again.
    It is all in the owners hand book which you will normally find in a plastic folder tucked in its little cubby hole up the back of the bottom glove box.

    Glad to help.
     
  8. Mike Dimmick

    Mike Dimmick Active Member

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    I think this may have changed in later model years. My car resets the Mileage counter on the MFD on filling up, but does not reset the accumulated average. My average is now for about 7,000 miles (and is around 56.8mpg [imperial] if I recall correctly, having been over 60 in September).

    Stupidly, I didn't get the two measures - by MFD and by tank - synchronized, or if I did, I didn't note which tank it was, so I can't do a true compare of accumulated MFD average to calculated average.

    The car was an ex-demonstrator and it must have been demonstrated to some real leadfoots, because the average when I got it was around 40mpg. After a month or so of steadily increasing average I decided to find out what I was really getting and reset it. That day I got a reported 65.3mpg over my journey to and from work. Nice, but I suspect there was a bit of error.
     
  9. qbee42

    qbee42 My other car is a boat

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    In later models, the miles figure resets on fill-up, but not the mileage. You have to hit "reset" to reset the mileage.

    Tom
     
  10. pnerd

    pnerd Junior Member

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    That may be so in yours.
    In my 2006 Prius, pressing the RESET soft-button has a different effect from the post-refueling auto-reset, as noted by a few other posts in this thread.
    Sure it isn't "rocket science", I agree, never said it was.
     
  11. patsparks

    patsparks An Aussie perspective

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    Hey, sorry I f***ed up!