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Sudden Significant Drop in MPG!!! 50 to 40 overnight!

Discussion in 'Gen 4 Prius Fuel Economy' started by PappyAdkins, Jun 21, 2022.

  1. PappyAdkins

    PappyAdkins Junior Member

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    Yes sir, I camped out (this last time) several months ago... probably several months after I changed out the battery & several weeks before the sudden change in mpg... basically, I changed out the 12v battery approx. 6 months before the sudden loss of mpg...
     
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  2. PappyAdkins

    PappyAdkins Junior Member

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    Question, I've read your post & tried to reset system using cruise control method (no luck)... have you came across any other method to reset it? (I have thought about taking it to the dealer, but from the sound of it no body seems to think your description of the issue is too valid... It is EXACTLY what I'm seeing! <Attention Prius Owners, I believe I have discovered a previously unknown Mechanism of Low MPG. | PriusChat>) BTW, I have connected my car to the OBD reader... there is NO Errors that have ever came up... I don't have access to the one that reads temps yet....
     
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  3. Doug McC

    Doug McC Senior Member

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    Out of curiosity: when camping are you using the car’s electrical systems, and if so, in what ways? Please be specific as possible. Thanks
     
  4. CooCooCaChoo

    CooCooCaChoo Senior Member

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    You can just leave the car on and the ICE will run every so often to charge the hybrid battery backup. Make sure you turn off the headlights though.
     
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  5. PappyAdkins

    PappyAdkins Junior Member

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    Basically you never turn off your ignition when you pull into your campsite. The Prius will keep radio (if you want), climate control, etc. running. It of course is in EV mode, the engine kicks in at idle for a few minutes every hour or so to charge up the battery. I tell people the Prius is basically a generator on wheels. There’s a whole group out there that camp or live out of their Prius for this reason. Hope that answered your questions. If not let me know.
     
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  6. bisco

    bisco cookie crumbler

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    yes, we have a whole forum on it, great applications, camping and emergency generator
     
  7. TheLastMojojomo

    TheLastMojojomo Active Member

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    I don't have any other methods for triggering the MAX EV State. It is the most frustrating and confusing problem ever and results in on average me losing $5 worth of gas a day on mail routes... taking mpg from 45 to 35 in my Gen 2. And literally no other Prius owner knows what I'm talking about. Which is why I'm on a quest to prove it.

    I just went to a dealer a couple weeks ago and talked about what I was experiencing... and they kind of just wrote me off but were impressed with my knowledge of the Prius. I told them I'd come back when I have proof.

    The only other user I've found who has recognized the scope of this problem is user @kirill626 in this post: Possible undiscovered performance and MPG issues with Prius v (lowercase v) Drove him crazy as well and many didn't believe him.

    I would get access to a Bluetooth OBDII device and use something like Dr. Prius to read temps and monitor data which seems like you're working on anyways.

    I'm working on getting a video out about this... Just finished writing the script yesterday and will be filming it shortly.

    Posted via the PriusChat mobile app.
     
  8. PappyAdkins

    PappyAdkins Junior Member

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    well for the record, this Prius owner knows exactly what you’re saying!!! Some have suggested I take it to the dealer, but I have read too many times where they took it in to the dealer & suddenly their mpg went down after dealer reset system. I was afraid I’d get same response as you if I did. I’ll check out the other user you mentioned.

    we will keep up the pursuit and continue helping the gas empires have record quarters. Looking forward to the video for sure. Wishing us the best of luck. Thanks for sharing. david
     
  9. Doug McC

    Doug McC Senior Member

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    Thanks, that does answer my question. When you say you don’t turn off the ignition, do you mean you leave it in the Ready mode (as though you were driving) or do you put it in ignition mode? Do the other members of your family also camp with you or elsewhere and use their Prius’ the same way?
     
  10. PappyAdkins

    PappyAdkins Junior Member

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    Ready mode I think… my Gen4 I just put it in park and leave it running. Think my dad has spent the night a time or two… but he didn’t make bed, just slept in front seat! Most use twin mattress in back, my wife and I use a full-size mattress and it fits nice in my gen4. Sometimes use our habitent sometimes just cover windows. We typically boondock in out of the way places. A couple of times at campgrounds. We use freecampsites dot net. I built a teardrop years ago; but camping in the Prius is just great in my book. Much better fuel economy and more stealth if you need it…

    it might be fun to join up with other Prius Campers… maybe we’ll have to startup a group or maybe find some groups out there.
     
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  11. GuyKrissy

    GuyKrissy New Member

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    Hopefully your problem has fixed itself. I know we're all paranoid our battery is going out. But poor gas mileage can usually be chalked up to something more rational, like our driving habbit.
    Prius is a very fickle car. It wants perfect weather, no weight and a cats paw on the gas pedal.
    But relax , my man, you got a toyota! Its gonna outlast a tesla. Boom! Lol
     
  12. PappyAdkins

    PappyAdkins Junior Member

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    Thanks for the reply, nope hadn’t fixed itself. I’m convinced it’s in the brain of MY car. Not habits. Not weather. Not the battery. Just a sudden change in my car only, not my wife or dad’s which have exactly same weather and similar driving habits. Every once in a while it works correctly for a bit. But at other times, with a fully charged battery, foot off pedal, coming up to a light, it will not go into EV mode other times (and always before) it would. With that being said, I still LOVE my Priuses. Just wish Toyota would admit issue and we could fix it. 40mpg is still better than 30 I’d get in most other vehicles of similar price range.
     
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  13. GuyKrissy

    GuyKrissy New Member

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    Ouch! Seems more serious than i thought.
    You should be getting much more than 40mpg on a gen4.
    Make sure youre driving in NORMAL mode. Not ECO.
    Disconnect the 12v battery for a couple hours. That should do a hard reset on the car.
    Also download the DR PRIUS app.
    Look thru the app and find the proper OBD scanner to use. You will most likely have to buy one off Amazon $30-50 range.
    Also...whats the mileage you have?
    My vehicle isnt as efficient as it once was.
    But with 100k, im still easily getting 52 in mixed driving. Gen4 prius2. Nimh
     
  14. GuyKrissy

    GuyKrissy New Member

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    On the DR PRIUS app....full disclosure , i have not used it yet. But plan to.
    Its supposed to give an estimate on the battery life left. Many people say its legit. Im spreading the word on good faith.
    Good luck, buddy. And keep us informed
     
  15. GuyKrissy

    GuyKrissy New Member

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    Hey buddy, also on the passenger side, back seat, theres some vents located on the base of the seat. That's where the battery breathes and cools. It should never be covered and theres a filter that needs to be replaced, behind the vent.
    The vent is part of the plastic base of seat.but easily snaps out and snaps back in. I think theres one plastic fastner and maybe 3 snaps.
     
  16. PappyAdkins

    PappyAdkins Junior Member

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    Thanks again GuyKrissy, yep since I camp in my Prius from time to time, I'm also in the group that "lives/camps in their Prius" and I preach the importance of the filter being cleaned/unblocked at all times! As far as the Dr Prius app, I'd like to get it too... Just haven't done it yet... As far as the 'eco/normal' mode & leaving battery off for a couple of hours, I haven't heard anyone say that yet. I will try both this weekend & let ya know.... Thanks again....
     
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  17. Toyota2

    Toyota2 Junior Member

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    a 10 MPG drop is large Brakes that drag could cause a loss in any car ,.You could try a low speed coast to see if car shimmy's to a halt
    as you say from a stop it goes into EV mode try driving 4MPH & see how long it stays in EV mode .
    Going down an incline is a natural EV mode . You might have a crimp break hose .
    I think if you could test all the fixable drag forces that could cause computerized non EV interference from a laymen's position you could come to a conclusion if its an interference related non computer .
    A way to look at situation is - - your system is telling you , something is causing the need for low end power to soon .
     
  18. John Light

    John Light Junior Member

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    I have a 2018 Prius 2. I now have 59400 mile on the odometer. Ok just got back from a trip from Denver to Chicago and back. New tires before I left. Was seeing the usual 55-60 mpg at 80 mph.
    Traded seats with my wife. When I got back I was running 43mpg at 78 mph and 38 at 80 mph. I hadn't watched the power screen much. That is my wife's favorite. I am noticing that at freeway speed 55mph and higher the battery never gets charged. Coming back the cruise was having problems maintaining a set speed. In the past cruise on caused the car to rapidly accelerate to a speed and held it. Now, when a speed is set it drifts down 1-2 mph below the setting and tries to get back there. On the last leg, with cruise set if I gave more pressure on the throttle, the speed dropped at first. Called the dealer today and their first appointment for service is Nov31 a month out. Next step is to get my scan tool out and then head to my old bosses's shop he was working on Prius's for a while. I welcome any thoughts and I will update as I find out more.
     
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  19. Toyota2

    Toyota2 Junior Member

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    To really see a fact go 60 and slip trans selector into B braking mode seems to be pure recharge when you coast
     
  20. Mambo Dave

    Mambo Dave Active Member

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    Let us know what you find out. I'm wondering if you had a battery cell go bad.

    If I tell the cruise control to stop pausing, mine gently goes back up to speed - not rapidly like some cars I've had.