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Mileage drop after new 12v and air filter question

Discussion in 'Gen 2 Prius Technical Discussion' started by CO100, Feb 16, 2010.

  1. CO100

    CO100 Junior Member

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    Last week I had my 12 v battery replaced on my 2007 Prius. At the same time the dealer replaced my air filter. Since then I can't get over 46 MPG when I was routinely getting 52-54 MPG.

    I've gone about 80 miles since last week.

    Called the dealer's service manager and he said its probably the new 12 volt. That it reset the mileage reader history and is now drawing from little info.

    But I routinely reset the mileage reader on the panel before the 21 volt was replaced (everytime I put gas in it).

    Does anyone know the technical aspects of the mileage reader. Does this sound like a reasonable account or do you think there is a real mileage drop. Should I push them to check something?

    They suggested I give it a couple months and call back if it doesn't improve.

    BTW, I drive the same route everyday, same gas in the gas tank, no air pressure problems. Its been cold before and after the visit last week.

    Any comments? I'm not sure what to do.
     
    #1 CO100, Feb 16, 2010
  2. Flying White Dutchman

    Flying White Dutchman Senior Member

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    maybe the 12 vol battery replacement reseted al the ECU's
    now it needs to start learning again how you drive and uptimum eff.
     
    #2 Flying White Dutchman, Feb 16, 2010
  3. dogfriend

    dogfriend Human - Animal Hybrid

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    I noticed a drop in MFD mileage for a couple of tankfuls when I disconnected my 12V battery to work on the driver's seat. I did it twice, and noticed the effect both times.

    However, since you had it at the dealer, they could have adjusted the pressure in your tires and if you had an oil change, they could have overfilled the crankcase. You should check both unless you have already.
     
    #3 dogfriend, Feb 16, 2010
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  4. CO100

    CO100 Junior Member

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    Oddly, I drove 2 hours to the airport two days ago, speedliy (60-79 mph) because I was late and my gas mileage was better than in town (49 mpg). I've been back a day and now I am getting 52 or 53, even close to 54 MPG. This is back to the old range. Just thought I'd post a follow-up for anyone with similar issues.
     
    #4 CO100, Feb 20, 2010
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  5. JimN

    JimN Let the games begin!

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    The dealer hooks up a battery tender when swapping out the 12v. Unless the original was dead the settings should have been kept. My first thoughts are deflated tires & overfilled oil.
     
    #5 JimN, Feb 20, 2010
  6. CO100

    CO100 Junior Member

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    Aha! What if I told you when I got the car back from the dealer, the clock had been reset. I guess that means they didn't use a batter tender. hmmm.

    I read a thread from an earlier post on a related issue. It said a technical manual discusses the MPG effects of losing 12V battery power. So it seems like this is a ECU "learning" problem... (but I'm not an excerpt...

    "Also, there is a section in the Tech Training manual that says that the HV ECU stores "Historical Data" to refine the calculations used for the Energy Screen. I am attaching a screen shot of the page. "


    The source for the quote above is a reply to a :rockon:post to this forum by Dogfriend in Feb 2007 Re: How/What Does the Prius' CPU(s) "Learn?"
     
    #6 CO100, Feb 22, 2010
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