appalling gas Mileage

Discussion in 'Gen 3 Prius Fuel Economy' started by Evan Perry, Apr 6, 2019.

  1. Evan Perry

    Evan Perry New Member

    Joined:
    Apr 6, 2019
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    Location:
    IL
    Vehicle:
    2010 Prius
    Model:
    I
    My Prius has an issue that has been getting much worse. The engine will not turn off unless the battery shows full. I get 25 MPG on the highway and about 30-35 city on a good day. I came here to see if anyone had a similar issue, not completely. However, I did find out about an app called DR. Prius. I have recently started to monitor the traction battery with it and have noticed what seems to be a high base voltage between 220V - 230V. When I accelerate it drops to around 180V, but it has dropped as low as 160V. When I brake it spikes the voltage to nearly 300V. It has been getting worse with time 'about a year now' but has been manageable, so far.

    I took it in for an oil change and its 100,000 mile service, in 2019. While explaining this issue with a tech he said that low MPG is common in winter months, which is true, But I still wanted to know if there was a problem since my mpg was lower than prior winters. I asked him to hook up the car and run a full system diagnostic scan of my car, mainly the hybrid system. He agreed. He also told me that there was a software update/patch. I agreed to it and am now regretting it. Since I got my Prius back I have noticed other system issues aside from the drastic drop in mpg. The other big issue is the tank capacity gauge seems to be malfunctioning. It wont go past 413 gallons till empty no matter if I put 7 or 9 gallons in the tank.

    I am curious if anyone here has or heard of a similar issue. I am thinking of taking it back to the dealer and having them run the test again, if it shows no issues then have them roll it back to factory software. It is almost as if the update damaged the battery, BMS, ECC or the Hybrid System Controller. Or I hope Toyota isn't trying to pull the same thing Apple did a few years ago with there older phones.
     
  2. maurices

    maurices Member

    Joined:
    Apr 22, 2010
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    Location:
    Sartell, Minnesota
    Vehicle:
    2013 Prius
    Model:
    Four
    I live in Minnesota and the winters are very harsh. The worst mileage I have gotten with either my 2010 or my 2013 was 38mpg.
     
  3. bisco

    bisco cookie crumbler

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    Location:
    boston
    Vehicle:
    2012 Prius Plug-in
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    Plug-in Base
    welcome!

    can you give us a rundown of your mpg's before they declined?

    there are many places to look for mpg problems on a prius, most are not in the service schedule.

    also, a history of your car would be helpful

    100,000 miles is right around the time 2010's egr circuit completely clogs, and the head gasket blows.

    is she burning any oil?
     
  4. royrose

    royrose Active Member

    Joined:
    Mar 21, 2009
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    Location:
    Foot of Pikes Peak
    Vehicle:
    2010 Prius
    Model:
    IV
    My Prius is just about the same age and mileage: 2010 with 95,000. Mine is running like new and I am due for that software update but waiting on that. I still get mpg in the 40's and got around 50 on good days even at this time of year, so your story is scary.

    Since you are new to PriusChat, you will see comments like those of Bisco (whose comments overall I respect) that EGR problems become severe at or soon after 100,000 miles but a few of us see that as potential problem that may take many more miles than 100,000 to become severe. (Lets not re-argue that issue). A middle of the road choice would be to check the condition of the easily accessible EGR pipe. Look for threads about the EGR circuit on PriusChat for more on this topic. I don't think that would explain your unusual battery issues.

    I agree that we need more info. Did your problems arise suddenly or slowly? What are your climate and driving conditions? Does it start up Ok and runsmoothly or is there any hesitation? Etc. Did the dealer find any diagnostic codes? Also, is there an independent hybrid shop anywhere near you where you can get a second opinion?

    If it is the battery and you have had your Prius serviced regularly at a dealer, Toyota might help on the battery replacement even though you are out of warranty due to the age of the vehicle.

    I believe that it is not possible to roll back the software. Let us know what happens.
     
    #4 royrose, Apr 7, 2019
    Last edited: Apr 7, 2019
  5. Evan Perry

    Evan Perry New Member

    Joined:
    Apr 6, 2019
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    Location:
    IL
    Vehicle:
    2010 Prius
    Model:
    I
    When I first got her, her mpg was the normal. After the first 2 years is when I started to notice the drop. It was then just a couple of mpg's so I wasn't that concerned. It was when I took it in for service at 70,712 I really started to notice things.for instance EV mode was now limited to 10 MPH instead of 25. The following winter when it got really cold the engine would start rough as if running dry. The summer of 2017 is when she started to burn oil at 112,602 miles.
    The update at 70,712 was "E0E-REFLASH MOTOR GENERATOR & POWER MANAGEMENT ECU-PRIUS"
    The latest update was at 134,805. "J0V RECALL, UPDATED POWER MANAGEMENT ECU."
    This is the one I suspect is at least partially responsibly for my problem.
    So to answer your question "royrose". My problem is like the first hill on a roller coaster, slow at first then a steep drop that makes you wish you were wearing brown pants. I do mostly highway driving with gradually dips and climbs, I use cruise most of the time also. When I start her up cold, she's angry for about 10 seconds the smooths out. No codes yet. I do plan on taking her in soon for them to run tests specifically for the hybrid system. Honestly I would wait on the update but that said if a safety update does come out, I would get it updated.
    I will definitely look into the EGR system. I will keep you guys updated and thanks for the info.
     
  6. royrose

    royrose Active Member

    Joined:
    Mar 21, 2009
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    Location:
    Foot of Pikes Peak
    Vehicle:
    2010 Prius
    Model:
    IV
    i thought you had just over 100,000. With your mileage over 134,800 EGR and head gasket problems are a real possibility. You may have multiple issues.
     
    Borninblue and mjoo like this.
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