I'm steadily losing mpg on highway. very hour or so it keeps going down further. Moving across coun

Discussion in 'Gen 3 Prius Care, Maintenance & Troubleshooting' started by Blurredforlife, Jan 1, 2023.

  1. Blurredforlife

    Blurredforlife Junior Member

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    So a few days ago I got a po101 code. No problem cleaned the sensor. The mpg seems normal driving around town. I'm moving across country so the pruis is loaded up. I started at around 42 mpg and each hour of highway driving I am losing mpg to the point its at 37. I pulled in for the night because it's steadily going down. I've searched threads but I'm honestly stumped. Could it be the sensor and low battery? I did leave bluedriver plugged in and it got its first sub zero blast of the year in Chicago resently. Maybe fuel pump?
     
    #1 Blurredforlife, Jan 1, 2023
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  2. Mendel Leisk

    Mendel Leisk Senior Member

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    For anyone else scratching their head, P0101 is for Mass Air Flow sensor.

    What cleaner did you use, one spec'd for MAF?
    Did check engine light go on, alerting you, and after the cleaning has it gone off?

    How much weight in the car?
    What's the temp where you're driving?
    What speed are you doing?
    Headwind, tailwind?
    Grade changes?
     
    #2 Mendel Leisk, Jan 1, 2023
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  3. fotomoto

    fotomoto Senior Member

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    Yes, typically mpg should rise on long drives like this as it eliminates the cold-start penalty to only the first startup of the day.

    Besides the vehicle itself, there are WAY too many variables to nail this down and one is direction of travel. Heading into colder weather is a big cause. Heading west from Chi-town? You'll be climbing for a long time.
     
    #3 fotomoto, Jan 1, 2023
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  4. Blurredforlife

    Blurredforlife Junior Member

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    #4 Blurredforlife, Jan 1, 2023
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  5. Blurredforlife

    Blurredforlife Junior Member

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    Exactly
     
    #5 Blurredforlife, Jan 1, 2023
  6. Blurredforlife

    Blurredforlife Junior Member

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    So I just swamped out the old sensor for a new one. I checked the battery and it looks like the original battery from the factory. Clean but japanese writing all over it. Bought a new battery. I'll guess we'll see. The thing that stumps me is that I've made this same trip many times with the same loaded vehicle and never lost milage. The website has been a great source of information by people who know.
     
    #6 Blurredforlife, Jan 1, 2023
  7. sam spade 2

    sam spade 2 Senior Member

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    That statement is grossly misleading.
    Carrying a heavy load and going faster than "normal" will NOT result in better gas mileage.

    Not enough data to say what he is seeing is not normal.

    AND how the indicted mileage reacts depends a lot on when it was last reset.
    If that average is over many days and many miles, the fluctuations will be less noticeable.
     
    #7 sam spade 2, Jan 1, 2023
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  8. CR94

    CR94 Senior Member

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    Headwinds increase fuel consumption, and so do low temperatures.
     
    #8 CR94, Jan 1, 2023
  9. Blurredforlife

    Blurredforlife Junior Member

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    So after replacing the sensor and the battery I was back to my normal mpg with moving..40.5 I drive around 550 highway miles. However the last two hours I started losing mpg again but at a slower rate this time. Again last night I went from 41. To 36.5 mpg. Every hour I would lose...41 40 39 38 37..I'm just at a loss unless my hybrid battery is slowing failing. I tested my smog check on my bluedriver..the smog readness check said my evaporative system wasn't ready after 550 miles of driving.
     
    #9 Blurredforlife, Jan 2, 2023
  10. Blurredforlife

    Blurredforlife Junior Member

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    I went from 40.5 the majority of the day to 38.5 the last two hours of driving
     
    #10 Blurredforlife, Jan 2, 2023
  11. sam spade 2

    sam spade 2 Senior Member

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    Head winds.
    Drastic temp drop.
    Speed increased.

    You are NOT resetting the fuel mileage monitor, are you ?
     
    #11 sam spade 2, Jan 2, 2023
  12. Mendel Leisk

    Mendel Leisk Senior Member

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    Yeah this minute-by-minute mpg status may be problematic, similar to watching your investment portfolio too closely.
     
    #12 Mendel Leisk, Jan 2, 2023
  13. fotomoto

    fotomoto Senior Member

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    I didn't say it was or would be "better". I said it should rise from the first tank of the day. Every reading could still be below EPA, for example. I also didn't speak in absolutes.
     
    #13 fotomoto, Jan 2, 2023
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  14. Blurredforlife

    Blurredforlife Junior Member

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    Indeed Ihaven't...Ive had 3 of these vehicles and have made these trips with the same conditions and never had my mpg drop under 40 mpg.
     
    #14 Blurredforlife, Jan 2, 2023
  15. Blurredforlife

    Blurredforlife Junior Member

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    I've made this same trip so many times for work. I've had 3 of these vehicles and never experienced this. Before I swapped sensor and battery it was at 41 mpg for hours and dropped steadily to around 36 for apparently no reason. I just didn't think this was something normal
     
    #15 Blurredforlife, Jan 2, 2023
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  16. Blurredforlife

    Blurredforlife Junior Member

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    Those are my exact thoughts...I'm stumped as to why
     
    #16 Blurredforlife, Jan 2, 2023
  17. sam spade 2

    sam spade 2 Senior Member

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    One more try and then I quit.

    First, you don't KNOW that the conditions are identical.

    Second, when you replaced the battery the MPG calculation probably got reset and now will be more sensitive to variations than it was before.

    Third, something else might have changed.......like a brake dragging.
    There may have been a seasonal change if the fuel formula.

    Lastly, your car is getting older. That very likely will happen with EVERY car if you drive it long enough.
    Some sooner, some later.

    Obsessing over things like this is not good for your health.
     
    #17 sam spade 2, Jan 2, 2023
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  18. Blurredforlife

    Blurredforlife Junior Member

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    So here is the update...used gum out and it seemed to cure a few of the problems. Certainly feels more responsive. Again thanks everyone for the advice and wisdom
     
    #18 Blurredforlife, Jan 21, 2023
  19. Fast track

    Fast track Junior Member

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    I’m experiencing on our 2015 Prius. 37 -38 mpg mixed city and Highway driving. Manual figuring to get the mpg. We have the original battery and MAF sensor has never been cleaned. We have just over 41,000 miles on it.
     
    #19 Fast track, Jan 23, 2023
  20. bisco

    bisco cookie crumbler

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    no need to clean the maf at 41k, has the mileage dropped?
     
    #20 bisco, Jan 23, 2023
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