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Coolant valve noise, but no code?

Discussion in 'Gen 2 Prius Care, Maintenance and Troubleshooting' started by Eric D., Apr 11, 2023.

  1. Eric D.

    Eric D. Junior Member

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    On a 2009 w/ ~96k miles, I hear a "see-saw" noise from the coolant control valve. I was hearing it intermittently in colder weather, but now hear it every drive after the car is warmed up. It will eventually stop, perhaps after 10 minutes (haven't timed it exactly). Heat works fine.

    I am surprised that the P1122 code has not been set. Does anyone know how many times the valve has to "hunt" before the code is set? I thought I saw it documented but now can't find it. I will probably preemptively replace the valve this year, but am curious as to why it's making the sound without the corresponding code.

    Thanks!
    Eric
     
    #1 Eric D., Apr 11, 2023
  2. PriusCamper

    PriusCamper Senior Member

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    It's the position sensor inside the valve that's failed. The noise is it trying and failing to do its one job... Fortunately there's lots of quality aftermarket versions of this part in the $40 range. I prefer the hose clamp method when swapping them out. Way less hassle than draining the whole system.
     
    #2 PriusCamper, Apr 11, 2023
  3. ChapmanF

    ChapmanF Senior Member

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    I would have to go look at the "detection condition" for that code to see if it even has anything to do with how many times the valve hunts. (The detection condition is shown in a box part-way down the first page of the repair manual section for a trouble code, and tells you exactly what conditions make the ECM set that code.) The code may be set in response to some other condition that hasn't occurred yet, even though the valve is clearly hunting.

    The codes are handy when they tell you about a problem you haven't otherwise noticed. On the other hand, when you can already tell something is busted, you don't have to wait for a code before fixing it. :)
     
    #3 ChapmanF, Apr 11, 2023
  4. Eric D.

    Eric D. Junior Member

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    Thanks for pointing me to the right place! The detection condition seems to be a percentage or a voltage off from normal, no mention of a number of tries. But I would think it would only retry if the sensor reading was abnormal… I guess not enough!
     
    #4 Eric D., Apr 11, 2023
  5. Rocinante

    Rocinante Junior Member

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    #5 Rocinante, Apr 16, 2023
  6. ChapmanF

    ChapmanF Senior Member

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    The sensor is a position sensor. It's how the ECM knows what position the valve is in.

    The ECM knows what position it wants the valve in, so it can look at the sensor reading and see if the valve is to one side or the other of the desired position, and if so, the ECM can send current to the valve motor in the indicated direction, until the sensor reading indicates the wanted position.

    If the sensor reading is something obviously bogus, like below 0.2 V or above 4.8 V, which is outside the design range, the ECM will set a code. That might mean a break or short in the wiring to the sensor, or a sensor that has failed in a really obvious way.

    If the sensor is giving a reading that is in range and looks like a real valve position, but it is wavering around and doesn't show the exact position the ECM wants, the ECM says "ok, my job is to move the valve until that reading is the position I want." So it does that.
     
    #6 ChapmanF, Apr 16, 2023
  7. rogerdpack

    rogerdpack Junior Member

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    Just had this, I think it means my new valve was bad...
     
    #7 rogerdpack, May 6, 2023
  8. mr_guy_mann

    mr_guy_mann Senior Member

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    #8 mr_guy_mann, May 7, 2023
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