knocking and surging

Discussion in 'Gen 3 Prius Care, Maintenance & Troubleshooting' started by Nashvilleguy, Jul 30, 2026 at 9:22 PM.

  1. Nashvilleguy

    Nashvilleguy Junior Member

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    My 2014 Prius 3 with 245K miles has been bucking and surging for some time. No check engine light, power and gas mileage are fine. The bucking only happens during steady speed. Not accelerating or decelerating. At around 30 to 35 miles per hour I hear a steady knock that corresponds with the bucking and continues as long as the bucking. A mechanic told me that was the switch that switches between the electric and gas modes. Could this be causing the surging and if not how much of a problem is this?
     
    #1 Nashvilleguy, Jul 30, 2026 at 9:22 PM
  2. bisco

    bisco cookie crumbler

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    have you cleaned the egr circuit?
     
    #2 bisco, Jul 30, 2026 at 9:26 PM
    Mendel Leisk likes this.
  3. Mendel Leisk

    Mendel Leisk MMX GEN III

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    How long have you had it?
     
    #3 Mendel Leisk, Jul 31, 2026 at 9:22 AM
  4. ETC(SS)

    ETC(SS) The OTHER One Percenter.....

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    Coolant level?


    I was thinking 'Prius Death Rattle' but that's usually a symptom that goes away while you're driving.

    Knocking can be looooots of things like: a motor mount, a cylinder knock from an incorrect air-fuel mix, water from the coolant loop getting into the engine, and all kinds of other things in a car that is basically at "end of life."
    Most 'knocking' is bad....
    Sometimes it REALLY bad.
    I'm thinking that your mechanic might be incorrect about "switching between gas end electric modes" because a wireless G3 (non-plug-in) is always in "gas mode" at 35MPH.
    Your "transaxle" which is actually called a 'power split device' that uses Motor Generators to charge the traction battery, start the car by spinning the ICE, and to drive the wheels or assist the ICE by providing additional power - on demand.

    I can see MG2 maybe causing the symptoms you are describing - and it's an easy fix!
    Just replace the [sic] transmission.

    I'm a little bit of a hard sell on this being the culprit though.
    You never mentioned what your mechanic wanted to do about it?
     
    #4 ETC(SS), Jul 31, 2026 at 10:08 AM
    Last edited: Jul 31, 2026 at 10:13 AM
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