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Found a major issue with the displayed MPG

Discussion in 'Gen 3 Prius Fuel Economy' started by Judgeless, Jun 4, 2012.

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  1. Judgeless

    Judgeless Senior Member

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    No this is not another thread that claims the display does not match the calculated.

    I am having issues with my 12V battery when I leave the car at the airport for a week. The battery gets drained and I have to jump start the car. I have an aftermarket alarm that has a feature that will auto start the car when the battery gets low to top it off.

    Last week I made another trip and left the car at the airport with the auto start option on. When I got back the car was dead again. I found something very odd. The display showed I drove 239.0 miles with an average MPG of 54.5. When I left the car it showed a half tank of gas to go. When I got back it showed one bar of gas left and it showed 38 miles left before empty.

    [​IMG]

    The huge issue is the CONS. MPG only works when the car is moving. If it burns gas when sitting it does not reflect on the display.
     
    #1 Judgeless, Jun 4, 2012
  2. F8L

    F8L Protecting Habitat & AG Lands

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    Are you sure? I could have sworn I watched it go down while sitting parked with the car in Ready mode.
     
    #2 F8L, Jun 4, 2012
  3. Judgeless

    Judgeless Senior Member

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    I did not watch it happen. When I got back I only had one bar on the gas gauge and the MPG's and miles driven are shown above.
     
    #3 Judgeless, Jun 4, 2012
  4. secondspassed

    secondspassed Member

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    In my Prius C I am positive I've seen the mpg go down when the engine comes on while I'm parked, for what it's worth.
     
    #4 secondspassed, Jun 4, 2012
  5. The Critic

    The Critic Resident Critic

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    +1

    This must be an issue with how the Viper alarm is setup to run the car.
     
    #5 The Critic, Jun 4, 2012
  6. Judgeless

    Judgeless Senior Member

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    That might be the case. I will keep and eye on the MPG's next time I remote start the car for awhile.

    I am wondering if that is what I draining my battery.
     
    #6 Judgeless, Jun 4, 2012
  7. jdcollins5

    jdcollins5 Senior Member

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    The mpg will drop rather quickly if you run the ICE while sitting still. The mpg is calculated the entire time the car is Ready, whether moving or not.

    What were the miles and mpg displayed before you left ?

    Are you sure the parking lot attendants did not take it for a joy ride :)
     
    #7 jdcollins5, Jun 4, 2012
  8. The Critic

    The Critic Resident Critic

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    If I remember correctly you are at almost 90k miles? It is possible that the 12v battery life is correlated to not only time but also mileage. Since you only started having the dead battery issue recently I doubt it is caused by the Viper unit.


    iPhone ?
     
    #8 The Critic, Jun 4, 2012
  9. DaveinOlyWA

    DaveinOlyWA 3rd Time was Solariffic!!

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    the MPGs most certainly go down if you are not moving and the engine is running.
     
    #9 DaveinOlyWA, Jun 4, 2012
  10. fuzzy1

    fuzzy1 Senior Member

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    I'd swear the same.

    Is the OP certain that the missing fuel disappeared through the ICE, and not through the filler door or a hole in the fuel tank with the assistance of a thief?
     
    #10 fuzzy1, Jun 4, 2012
  11. milkman44

    milkman44 Active Member

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    Sounds like it's time for a new battery.
     
    #11 milkman44, Jun 4, 2012
  12. Judgeless

    Judgeless Senior Member

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    The mileage and MPG’s was the same as when I left the car. The only difference was the gas was no longer in the tank.
     
    #12 Judgeless, Jun 4, 2012
  13. Judgeless

    Judgeless Senior Member

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    I am at 84,000 miles now. This is the third time this summer it happen. Each time I was on a 1 week trip and it died at the airport. I almost got a battery last week. Maybe all the bumping around hitting pot holes caused a bad cell in the battery.
     
    #13 Judgeless, Jun 4, 2012
  14. Judgeless

    Judgeless Senior Member

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    That is exactly how it appears. There are no pry marks on the gas door. This happen 2 days ago. I keep the car in an enclosed garage. If there was a leak I would smell it.
     
    #14 Judgeless, Jun 4, 2012
  15. jdcollins5

    jdcollins5 Senior Member

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    That is odd. Since the gas is gone it must have run the ICE quite a bit to burn a half tank of gas. But how it did not lower your mpg is really odd.

    I agree with it probably time to replace your 12V battery.
     
    #15 jdcollins5, Jun 4, 2012
  16. fuzzy1

    fuzzy1 Senior Member

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    During the 2008 gas price spike, one of the fuel theft tricks was to drill a small hole in the tank. This was most common on high clearance vehicles (trucks and SUVs) due to the ease of crawling under them, so it seems unlikely for a Prius.

    Before shotgunning the 12V battery, measure it.
     
    #16 fuzzy1, Jun 4, 2012
  17. secondspassed

    secondspassed Member

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    When your alarm "starts" the car it sounds like the car's computers aren't being properly notified, not a problem with the stock behavior.
     
    #17 secondspassed, Jun 4, 2012
  18. szgabor

    szgabor Active Member

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    Someone drove your car that simple !!!! IF the engine can go on the smart key system most be disabled or the key somewhere in the car ...

    This would explain it ... what happened I do not know...
     
    #18 szgabor, Jun 5, 2012
  19. kajung2k

    kajung2k Junior Member

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    Chalk the inner tire and line it up with the ground. When you get back see if the inner chalk mark matches.
     
    #19 kajung2k, Jun 5, 2012
  20. fuzzy1

    fuzzy1 Senior Member

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    This explanation does not fit the pictured TripB / CONS figures, unless the trip meter was reset sometime later than the last refueling.
     
    #20 fuzzy1, Jun 5, 2012
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