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2015 Prius mileage drop to 23 mpg

Discussion in 'Gen 3 Prius Fuel Economy' started by Dr.E777, Apr 6, 2022.

  1. Dr.E777

    Dr.E777 Junior Member

    Joined:
    Oct 6, 2014
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    Location:
    Los Angeles, CA
    Vehicle:
    2014 Prius
    Model:
    Five
    My 2015 Prius mileage fell from 44 to 35 in January, and now it’s averaging 23 mpg.
    New plugs, air filter. Tires are excellent and properly inflated.
    Recently all the error codes went off and the dealer said it was a wheel sensor. Replaced that and the error codes went away.
    But the mileage continues to fall…

    No lights on the dash. Dealer says too bad…won’t look at it unless an idiot light comes on.
    Thoughts?
     
    #1 Dr.E777, Apr 6, 2022
  2. bisco

    bisco cookie crumbler

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    Plug-in Base
    how many miles on her?

    are you calculating mpg at the pump miles/gallons?

    has anything changed, new tires, trip length, frequency?

    how is the 12 volt health?

    air and cabin filter?

    does the car gide freely if you put it in neutral at 10mph?

    any of the wheels warm to the touch after a long drive?

    brke caliper pins lubed properly?
     
    #2 bisco, Apr 6, 2022
    Last edited: Apr 6, 2022
  3. ASRDogman

    ASRDogman Senior Member

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    What type of plugs? They might me the chinese copies and they are falling apart.

     
    #3 ASRDogman, Apr 6, 2022
    Dr.E777 likes this.
  4. Dr.E777

    Dr.E777 Junior Member

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    Model:
    Five
    Yes.
     
    #4 Dr.E777, Apr 7, 2022
  5. Dr.E777

    Dr.E777 Junior Member

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    Five
    NGK. Good ones. My friend runs a big garage. His guy looked it over and says the car is fine. He suspected the Hybrid drive.
    he was shocked the Dealer only works off idiot lights and codes.
    I’ll try a different dealer service that was friendly and helpful when I called.
     
    #5 Dr.E777, Apr 7, 2022
  6. bisco

    bisco cookie crumbler

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    has the egr circuit been cleaned?
     
    #6 bisco, Apr 7, 2022
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  7. drbtz

    drbtz Member

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    Location:
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    Vehicle:
    2015 Prius
    Model:
    III
    Maybe invest in an OBDII bluetooth reader and take a peak to see what the modules are at voltage wise.

    This particular one is cheap ($13USD at time of writing) and is recommended by Jack aka Dr. Prius.



    Outside of some hybrid driver components I'm not sure what else would be causing the sharp drop. If plugs are brand name (you said they are), filters are not clogged (they shouldn't be), and wheels rotate freely (no seized calipers here), then I don't know what else would cause this.
     
    #7 drbtz, Apr 8, 2022
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  8. Mendel Leisk

    Mendel Leisk Senior Member

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    Location:
    Greater Vancouver, British Columbia, Canada
    Vehicle:
    2010 Prius
    Model:
    Touring
    The stock plug is SC16HR11 (supersceding SC20HR11). What kinda NGK's, what part number? Where'd you get them? Did anyone pull one of the plugs and check them? When did that plug change happen?
     
    #8 Mendel Leisk, Apr 8, 2022
    bisco likes this.
  9. mikeflores2000

    mikeflores2000 Junior Member

    Joined:
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    Location:
    Merced, CA
    Vehicle:
    2010 Prius
    Model:
    IV
    My MPG started dropping after 100k miles.
    My nephew has same issue with his 2016 Prius.
    Likely culprit: burned, dirty ATF WS fluid.
    Why? After change my nephew reports
    4 to 5 MPG improvement.

     
    #9 mikeflores2000, Apr 8, 2022
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  10. Dr.E777

    Dr.E777 Junior Member

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    2014 Prius
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    Five
    I went to a different dealer who was very helpful. Sold me Denso plugs and a shop guy walked out to my car and cleaned the MAF sensor in about 60 seconds and wouldn’t charge me.
    Swapped the plugs and mileage is up to 44. So, between a dirty MAF and non-Denso plugs, not sure but that did the trick for me
     
    #10 Dr.E777, Apr 9, 2022
    wr69, ASRDogman and Mendel Leisk like this.
  11. mikeflores2000

    mikeflores2000 Junior Member

    Joined:
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    Location:
    Merced, CA
    Vehicle:
    2010 Prius
    Model:
    IV
    I had dealer replace plugs and still 33 mpg. Maybe I didn’t clean MAF sensor correctly or something else like bad transmission.
     
    #11 mikeflores2000, Apr 9, 2022
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