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Weird P1121 after valve replaced

Discussion in 'Gen 2 Prius Technical Discussion' started by Ruming, Nov 27, 2020.

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  1. ChapmanF

    ChapmanF Senior Member

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    The circuit inside isn't very complicated, not really different from the position sensors used to locate the doors in the HVAC, etc. Given the trouble codes / INF codes available and a little poking around with a meter, it wouldn't be hard to pinpoint exactly what was causing the issue. But not everyone goes that far into it.
     
    #21 ChapmanF, Feb 8, 2021
  2. Ruming

    Ruming Junior Member

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    Yes, the code pops up right after clearing every time.

    Posted via the PriusChat mobile app.
     
    #22 Ruming, Feb 10, 2021
  3. Ruming

    Ruming Junior Member

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    I opened the Dorman valve for a postmortem. The valve itself isn't stuck. I don't have measurement but given the gears I believe it is good. Will Keep it until I have power supply and oscilliscope, or if anyone in Vancouver area interested.

    Posted via the PriusChat mobile app.
     
    #23 Ruming, Feb 10, 2021
  4. ChapmanF

    ChapmanF Senior Member

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    The position sensor 'circuit' is just a potentiometer. Shouldn't need anything as sophisticated as an oscilloscope to see how it operates.
     
    #24 ChapmanF, Feb 11, 2021
  5. tidesofthesky

    tidesofthesky Member

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    I think I remember it operating on a 5v reference, right? Should be easy to run 5v to it off a wall wart and check the output voltage at the different positions. Pretty sure the manual lists what the values should be for each valve position. I tested the signal in car by probing the ecu connector behind the glove box as detailed in the manual.
    Posted via the PriusChat mobile app.
     
    #25 tidesofthesky, Feb 17, 2021
  6. mr_guy_mann

    mr_guy_mann Senior Member

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    Yep, just 5V reference, reference ground, and signal. You might see the problem with a DVOM, or not. Depends on how big the bad spot is and where it is, and how "fast" your meter is (helps to have one with a bar graph display). I have seen some that would work great every time I tested it with Techstream- voltage at every position was fine- moved as commanded. Still set a code 2 days later. Only saw that glitch with a scope. YMMV.
     
    #26 mr_guy_mann, Feb 18, 2021
  7. Ruming

    Ruming Junior Member

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    Yes, that's where the scope comes valuable.

    I'm just curious whether it is the poentialmeter or the mechanical part that goes wrong. If the poentialmeters are the bottleneck, they can use better quality ones, instead of ruining the whole valve.
     
    #27 Ruming, Feb 19, 2021
  8. mr_guy_mann

    mr_guy_mann Senior Member

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    I think I have done 3 on various Gen2's. On this very small sample all had been potentiometer faults.

    The engineers (and/or bean counters) could have / should have used better quality parts - but didn't.

    Posted via the PriusChat mobile app.
     
    #28 mr_guy_mann, Feb 20, 2021
  9. Ruming

    Ruming Junior Member

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    Not having seen your post, I realized same thing this afternoon. When parked, the sound of valve operation of genuine part is exactly the same as Dorman.

    What a stupid decision making from engineering point of view!
     
    #29 Ruming, Feb 22, 2021
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