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Poor MPGs following Battery Swap

Discussion in 'Gen II Prius Main Forum' started by moshe_levy, Jan 21, 2012.

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  1. moshe_levy

    moshe_levy Junior Member

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    Swapped my dead OEM battery for an Optima a few days ago. In the 200 miles since, I'm averaging 27.3 MPG according to the computer. Usually I'm in the 40-41 range as I do alot of highway. I'm wondering if there is some resetting or reflashing I'm supposed to do when swapping a battery - for example on my motorcycle, I need to refresh the throttle position sensor when swapping a battery or response and mileage suffers until the system self corrects. Anything like that here, or is it just a spate of bad luck I'm having?

    -MKL
  2. uart

    uart Senior Member

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    Hi Moshe, that's a pretty big hit. Sometimes the displayed MPG is a little off after the "historical data" is reset (and it takes a while to rebuild that data). I'm not sure if that can account for your MPG hit, but try checking your MPG manually when you fill up.
  3. cnschult

    cnschult Active Member

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    and do you know how to go into maintenance mode to check the voltage of the new battery? perhaps the new optima wasn't very charged when you received it, and in the winter you are running lots of accessories like radio, front and rear defrost, headlights, etc so if your trips are short the alternator may not have much time to recharge your new battery. but plz do check the voltage following procedures found on priuschat
  4. cnschult

    cnschult Active Member

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  5. cnschult

    cnschult Active Member

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  6. cwerdna

    cwerdna Senior Member

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    Nope, about the only things that I can think of that need might need to be reset are power window initialization, radio presets and settings disabling the backup beep.

    http://priuschat.com/forums/gen-ii-...-answer-these-questions-esp-if-youre-new.html

    Dumb question... before when you got "40-41 range", were you resetting the MFD after each fill up? I don't know the MFD behavior that well since I ALWAYS reset it after each fill. For all I know, you might've been getting "27 mpg" for a long time and not realize it due to lack of reset. Disconnecting the battery reset it for you.
  7. moshe_levy

    moshe_levy Junior Member

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    Yes, I always reset the MFD at each fill. And I fully charged my Optima myself before putting it in. I'm going to use this tank up and start fresh, and see what happens.

    -MKL
  8. bisco

    bisco cookie crumbler

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    someone else got a bad optima and they sent him a new one.
  9. moshe_levy

    moshe_levy Junior Member

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    I'm happy to report the problem self-corrected. Filled the tank again, reset the MFD, and logged another 250 miles today. 39.8MPG, which is fine considering it was all highway in under +28F, with 5 people inside and the AC on (for defrost). We're back on track!

    -MKL
  10. uart

    uart Senior Member

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    The prius stores "historical data" on miles traveled and gallons added that it uses to improve the raw MPG calculations (that are based on the metered fuel injected).

    I had the same problem when I first got my Prius a few years ago. It had been reset by the dealer and it took a while before the reported fuel efficiency matched the actual (that I was getting from manual calculations).

    It might slowly improve even more over the next few tanks. That's what mine did.
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