225k lower mileage, ICE engine running more often 2009 Prius

Discussion in 'Gen 2 Prius Care, Maintenance and Troubleshooting' started by Cheffaz, Aug 2, 2021.

  1. Cheffaz

    Cheffaz Junior Member

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    2009 Prius, First i changed spark plugs about 5k miles ago, second I use Hybrid assistant to check the hybrid battery and the cells seem to be fine. I have a new Optima Yellow top battery changed 10k ago.

    Now it seems the ICE engine is running more and I gas mileage is way down like by 7 mpg, any ideas where to start? Inverter? HV Battery? bad spark plug? help please
    and
    Thank You.
     
  2. rjparker

    rjparker Senior Member

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    No codes or lights?

    The first thought with that mileage (high in my opinion) would be the hv battery. But I would not spend the money without a proper diagnosis first. Some like the Dr Prius app to read individual battery module voltages and parameters along with its paid version for a capacity estimate.
     
  3. sam spade 2

    sam spade 2 Senior Member

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    You can not necessarily trust the results of that app you are using.
    Most likely the HV battery is getting weak or some connections are corroding.
     
  4. JC91006

    JC91006 Senior Member

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    During the summer months and with heavy AC usage, what you're experiencing seems quite normal. If you have the same issue when the weather cools and without heavy AC usage, then you can start looking for solutions to an actual problem.
     
  5. PriusCamper

    PriusCamper Senior Member

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    Dr Prius App gives accurate reading and you can trust that part of the app... The battery test features however are not helpful or accurate enough to bother with.
     
  6. TheLastMojojomo

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    See my low mpg mechanism comment I made on Reddit describing low mpg resulting from a 12v disconnect.

    You can also view a similar comment on PriusChat. I'm currently working on a full post describing this mechanism and should be done soon.

    Basically what happens after a 12v disconnect is the Hybrid Control ECU needs to relearn certain parameters that are triggered by a certain commute style to use EV mode aggressively again.

    You can become locked in this low mpg state forever if you don't do the right commute style.

    Nobody else knows this low mpg mechanism exists besides me. Not even the most knowledgeable members of PriusChat.

    The details of how to know you're being effected by this low mpg mechanism and how to test for it are in the linked posts.

    Posted via the PriusChat mobile app.
     
    #6 TheLastMojojomo, Aug 2, 2021
    Last edited: Aug 2, 2021
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