P261C appearing in hot weather.

Discussion in 'Gen 3 Prius Technical Discussion' started by Imran nazir 79, Jun 8, 2025 at 11:43 AM.

  1. Imran nazir 79

    Imran nazir 79 Junior Member

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    Hello everyone. I am facing a strange problem. My prius 2014 would pop up Engine sign with P261C in scan in a hot weather about 40°C. However in morning and in evening it never happens. I have changed 2 to 3 water bodies and the running is also pretty fine...Secondly I have noticed, it happens when I switch on air conditioning.
    Any exact diagnosis will be of a great help I deed.
     
  2. ChapmanF

    ChapmanF Senior Member

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    I assume by "water bodies" you mean what I would call water pumps?

    Where have you obtained the water pumps you have installed?

    Do you have access to a scan tool that can show you the target and actual water pump RPM while driving?

    Do you have access to an oscilloscope?
     
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  3. Tombukt2

    Tombukt2 Senior Member

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    Yep more W AC on . Maybe used pumps ! Take the plastic plate off see the round thing that spins . ? White plastic peeling . Bingo .make it so pump no move it. part 35 online
     
  4. Imran nazir 79

    Imran nazir 79 Junior Member

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    Yeah the water pump rather coolant pump, yes I got it scanned and checked it's target and real RPM, the RPM obtained have been quite higher that the target, one thing I ve notices is that while keeping the AC off, I can run the vehicle as long as I can even in extreme hot,
    What I wanna know is what is exactly the relationship between an air conditioning and engine cooling system?
    Is the ECU same?
    Any relay which is common in the path and causes coolant pump go off after getting heat up or else.
     
  5. ASRDogman

    ASRDogman Senior Member

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    The condenser gets hot. And that hot air gets blown across the radiator.
    When the ac is running that is. So when it's off, the air going across the radiator is a lot cooler.
    Any way you look at it, the car is overheating. Maybe the fans are not blowing? But likely the
    coolant pump is failing.


     
  6. Tombukt2

    Tombukt2 Senior Member

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    You've just doubled or worse the load on cooling system very simply put. This must be all in town driving .?