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
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  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
  5. BiomedO1

    BiomedO1 Senior Member

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    Has ALL maintenance been done in a timely manner? Full synthetic oil changes? What is the normal operating temperature? Was the electric water pump ever changed? Have you ever put injection cleaner in your tank? Are the motor mounts intact or been checked?
     
    #5 BiomedO1, Jul 31, 2026 at 12:07 PM
  6. CR94

    CR94 Senior Member

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    Has it done that the entire time you've had it?
    Possibly coincidental, but that's around the speed at which mine is indecisive whether to run on battery or engine power.
    There is no literally noisy switch..
     
    #6 CR94, Jul 31, 2026 at 7:39 PM
  7. Nashvilleguy

    Nashvilleguy Junior Member

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    Thanks for the replies, I purchased the car in 2018 with around 64K miles. It was a originally purchased in Pennsylvania, There was gravel and dirt under the wheel covers from driving in show. I was aware of the EGR issue but forgot to put into the thread. I have done all oil changes with synthetic, replaced the plugs and also put injector cleaner in it. The mechanic wanted $2100.00 to clean the EGR which I think was his way of saying not to do it. I have done nothing else to it except tires and brakes. Two calipers were frozen and replaced. It still has the original starter battery, at least to me and the original hybrid battery. Cleaning the EGR system (which according to the videos I've seen that include removing the intake manifold) looks like a lot of work for a car this age. I will investigate a motor mount problem. Never overheated or lost coolant. But I will check on the circuit.
     
    #7 Nashvilleguy, Aug 5, 2026 at 2:03 PM
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  8. ColoradoBoo

    ColoradoBoo Senior Member

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    So the eCVT transmission has never been serviced? With other types, with high-mileage, folks advice not to mess with it as it can cause issues but I haven't heard that on the eCVTs on Toyota's so might be smart to get that VERY old transmission fluid changed out. (It's almost as easy as an oil change so shouldn't be too expensive.)
     
    #8 ColoradoBoo, Aug 5, 2026 at 2:08 PM
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