Water valve controller disasembly

Discussion in 'Gen 2 Prius Technical Discussion' started by Dion Kraft, Aug 22, 2025 at 1:09 PM.

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  1. Dion Kraft

    Dion Kraft Member

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    Being a very lazy driver who does no maintenance work on my own vehicle (although trained to maintain MTA buses and worked in a Electric utility company Ca's 2nd largest) I suspect that most of these problems are from debris in the coolant starting to clog the coolant system. I just got my three Prius manuals today ($200) upon which I researched the P1121 code along with its other relative DTCs and every one of them almost has CLOGGED water passages as a culprit in their diagnosis. As they say..its always the simple things that trip you up as that my motto when into diagnosis procedures. I only wish the water valve was made of clear plastic kinda like the clear engine toy when i was a kid so you can see what is going on within. What I want to do now is to take off the port cover and free it up..seal it up and end up reinstalling it and see what happens. Ofcourse theres the new 2 month old valve..I would have to take it apart and see if the big gear is stuck or not. Some of this will drive you to a drinkin'...and i do not drink !
     
    #21 Dion Kraft, Aug 23, 2025 at 2:47 PM
  2. Dion Kraft

    Dion Kraft Member

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    The gear to rotate to position the valving rotates but has stops so it does not revolve 360. One of the video's shows this when the Youtuber split the inner case to show the valving scheme and the seals of those ports.
     
    #22 Dion Kraft, Aug 23, 2025 at 2:59 PM
  3. Tombukt2

    Tombukt2 Senior Member

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    I bet it's not clogged my manual set is 4 or 5 books black and green colors . Taken plenty of these out . I've air here and in low out coolant passages on autos all the time seen big clots of shiet hot the wall as I do. It . Never in any model of Prius . I do not know why. Unless stop leak added . I guess I been lucky not to have worked on one those I guess.
     
    #23 Tombukt2, Aug 23, 2025 at 3:23 PM
  4. Tombukt2

    Tombukt2 Senior Member

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    I'd love to hear you bleed a big load of snot out a you're cooling system or valve .
     
    #24 Tombukt2, Aug 23, 2025 at 3:23 PM
  5. gdanner

    gdanner Member

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    Got that! Thanks!

    Because the valve has a mechanical stop this means the controller ECU is capable of driving the motor in both directions by reversing the polarity of the voltage which feeds it.

    Important: Do not use a high powered 12v source for testing the valve with 12V applied directly to the motor wires (black and red). This might strip the plastic gears when the valve hits the mechanical stop (or if the valve is totally stuck in one position). I expect normal operating current is <1 amp. Connecting a conventional (incandescent) 12V brake light bulb in series with the motor while testing should be sufficient protection. The brightness of the bulb indicates how much drag there is. The bulb should be dim when the valve is rotating and get brighter when the valve hits the mechanical stop. I'll test this and post my result.

    Another testing idea which came to me: Observing +/- polarity at the motor drive wires tells which direction it is rotating. I might cobble together a super-simple tester from a pair of LEDs wired back-to-back in parallel along with a series resistor. There should be a consistent pattern of LED blinking when the valve operates properly. However, if the motor is stalled by a stuck valve I would expect the polarity to rapidly fluctuate between + and - while the ECU attempts to get the valve to rotate. If the position sensor switch has dirty contacts the + and - may also randomly reverse while the ECU tries to get the valve into the desired position. Off-topic note: simple LED testers are often used for troubleshooting "inverter" mini-split air conditioners. Such testers have 6 LEDs in them. Because the compressor motor in these mini-split air conditioners receives 3-phase power at a variable frequency, the pattern and speed these 6 LEDs blink at tells a lot about what is happening inside the unit.
     
    #25 gdanner, Aug 23, 2025 at 5:58 PM
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