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Prius MPG Drop - Master checklist

Discussion in 'Gen 4 Prius Fuel Economy' started by deathmage, Nov 10, 2022.

  1. deathmage

    deathmage Junior Member

    Joined:
    Apr 23, 2017
    8
    3
    0
    Location:
    Los Angeles ca
    Vehicle:
    2017 Prius
    Model:
    Three
    At around 35k, my 2017 Prius MPG dropped from 60-65mpg to 47mpg. I've been into extreme car modification for decades and I thought this would be a simple fix. I live in Socal and the weather only fluctuates from 65-85 on average. I started with the simple fixes first - reflash the ecu, check the tire pressure. Nothing. Rubbed my chin and took it to a tire shop and got a rotation. Still no change in MPG. Ok.. so I took it up a notch. Replace the air filter with K&N.. nope. Replace the cabin filter.. nada. wth. Nothing installed on the exterior to create wind-drag. I was frustrated at this point and took it up another notch. Replace the 12v battery with a brand new one from the Toyota dealer. This is usually the last step for many and often times it fixes the issue. For me, still nothing. I didn't notice any difference in the frequency of engine kicking in. I believe in 'if you throw enough money at it, you can fix the problem.' So I went and replaced all 4 tires (my treads were at 20%, but had some cracks on the walls). This still didn't fix the issues. My last ditch effort was to clean the fuel injectors. Still didn't change anything. I swallowed my pride and started digging deep into the forums for answers at this point, but still couldn't find anything worth while. So exchanged it for a 2022 Prime XLE, lol. I work from home, so I'll be filling up around 5x times a year. With a $6.50 average gas price in socal, this is awesome. Here's a check list for MPG drop. for 90% of you, one of this will solve your issue. Order from simple to more aggressive.

    - Check Tire Pressure
    - Rotate tires
    - Temp drop or fluctuation?
    - Elevation change?
    - States with extreme weather - try thinner synthetic oil in the winter and thicker in the summer
    - disconnect the battery to have your ecu re learn your driving habit
    - Change air filter. Change cabin filter
    - Newly installed roof rack or other culprit of wind-drag
    - Change all 4 tires
    - Change the 12v battery (often times this fixes the issue)
    - Clean the fuel injectors (not using injector cleaning solutions, but having the shop clean it)

    desperate attempts
    - replace transmission oil (dirty oil can interfere with shifting)
    - clean or replace O2 and MAF sensors
    - change spark plugs.
    - clean throttle body

    very lastly, it can be your electronics, which isn't common.
     
  2. deathmage

    deathmage Junior Member

    Joined:
    Apr 23, 2017
    8
    3
    0
    Location:
    Los Angeles ca
    Vehicle:
    2017 Prius
    Model:
    Three
    Also, running AC will hurt MPG by 3-5, but not by 10+.
    There's a small possibility that my main battery was wearing out, but it only had 35k miles.
     
  3. bisco

    bisco cookie crumbler

    Joined:
    May 11, 2005
    108,166
    49,166
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    Location:
    boston
    Vehicle:
    2012 Prius Plug-in
    Model:
    Plug-in Base
    check for brake drag
     
    ColoradoBoo and Mendel Leisk like this.
  4. Mendel Leisk

    Mendel Leisk Luddite

    Joined:
    Oct 17, 2010
    55,014
    38,419
    80
    Location:
    Greater Vancouver, British Columbia, Canada
    Vehicle:
    2010 Prius
    Model:
    Touring
    And recent tire replacement, will get you every time...
     
    Louis19 likes this.
  5. ColoradoBoo

    ColoradoBoo Senior Member

    Joined:
    Jul 19, 2019
    936
    615
    4
    Location:
    Monument, Colorado USA
    Vehicle:
    2017 Prius
    Model:
    Two
    Years ago, I asked a Toyota mechanic about using fuel injector cleaners in my vehicles. He said I don't have to worry about that if I use gasoline from "Top Tier" gas stations. There's one near me so, now, I only fill-up from there, even if their price is a bit higher (it usually isn't, though).

    This website helps you find Top Tier stations and there's even an APP for your phone you can download.
    https://stationfinder.toptiergas.com/
     
    amos likes this.
  6. Louis19

    Louis19 Active Member

    Joined:
    Feb 4, 2022
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    Location:
    Laval Québec Canada
    Vehicle:
    2022 Prius Prime
    Model:
    Upgrade
    Yep, you are right . Just changed my Écopia for 4 winter tires and steel wheel for winter (mandatory where I live for the 1 december) and got a 10% dip in my EV range.
     
    Mendel Leisk likes this.
  7. jyii07

    jyii07 Junior Member

    Joined:
    Jul 21, 2020
    39
    19
    0
    Location:
    NYC
    Vehicle:
    2016 Prius
    Model:
    Four
    I'm going through the same exact issue as you.. Tried all the above EXCEPT cleaning out the MAF sensor and hoping thatll fix it. Its a 2016 with 133k+ miles so my other thought is the hybrid battery giving out but i'm hesitant on believing it because of the long term durability of it reported by others..
     
  8. douglasjre

    douglasjre Senior Member

    Joined:
    Sep 13, 2008
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    Location:
    Orlando, FL
    Vehicle:
    2010 Prius
    Model:
    ----USA----
    How did u reflash your ecu