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NOT Normal P Lock Malfunction - ONLY Happens Over 80 Degrees. Never When Cooler

Discussion in 'Gen 2 Prius Care, Maintenance and Troubleshooting' started by Rock_Star, May 25, 2024.

  1. Rock_Star

    Rock_Star Junior Member

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    Thanks for the explanation. That all makes sense. So it seems that by my readings there's an open circuit in PCON and PPOS. Still have no idea what the fix is, unfortunately.

    I actually found a Prius specialist about an hour from me. They know the P con error, but have never heard if it being caused by heat like mine does. I'm taking it there next Wednesday. They'll do a diagnostic for $180 and we'll go from there. They have a bunch of Gen2 parts and ECUs in stock for $50, so if it's one of those they should be able to swap it out for me. Hopefully!
     
  2. Rock_Star

    Rock_Star Junior Member

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    SOLVED!!!!

    I took it to a local Prius specialist and they eventually found a bad wire to the transmission resolver plug. They said it was very difficult to find, that they'd OHM'd every wire multiple times, and it took them a couple of weeks of testing to determine that was the issue. Once they fixed that, the P lock error went away.

    But apparently, they fried the parking brake control module in the testing/fixing process, so when they turned the car on it would short out and fry an ECU. It took them a couple of weeks to figure out that was the issue, but once they replaced the parking brake control module then the car was all good.

    I highly recommend autobeyours.com / Frontier Automotive in Scottsbug, Indiana. They were very fair with pricing, considering how much time they put into it. They're all great and friendly and they are an honest shop. They specialize in Prius, but work on all makes and models too.
     
  3. pasadena_commut

    pasadena_commut Senior Member

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    Glad you finally got it fixed.

    I shudder to think what the shops near me would charge for weeks of testing.
     
  4. ChapmanF

    ChapmanF Senior Member

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    Those are good folks. But are you positive they said "parking brake control module"? Pretty sure in a gen 2 that's not a thing.
     
  5. Tombukt2

    Tombukt2 Senior Member

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    I've heard about this resolver issue before somewhere probably right here That's why for this PLock malfunction it is pretty much mandatory to have the manual or you've done this hunt before and you know what's involved because I'm sure that's like a 34 page to do for this p lock business It must be one of the longer reeds and testings.
     
  6. Rock_Star

    Rock_Star Junior Member

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    I'm sure they'd rape you out there for it. Many places here probably would too, even though the labor rate is much lower here.

    I'm sure glad that it's finally fixed! Thanks for your help troubleshooting earlier.
     
  7. Rock_Star

    Rock_Star Junior Member

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    My bad. I had too many things floating in my head when I wrote that. I meant that they fried the thing behind the black round cover at the back of the transmission. I think that's called the shift actuator? We discussed how they got that off and he said Snap-On Tools makes a specialty tool that allows you to get those bolts out and he said it costs $395 I think!

    I think that's right anyway. I didn't write down what he said and I'm going from memory.

    Thanks for your suggestions on it earlier!
     
  8. Rock_Star

    Rock_Star Junior Member

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    Yes, it's a complicated issue potentially since there are several things that can cause that error. I had the manual and did the steps and found there was a likely ground fault sometimes, but the circuit was too complicated and had too many connections for me to figure it out.

    And made more difficult to find because the error only happened when the outside temperature was over 84 degrees! The wire wasn't completely cut or anything else that was easy to find. The heat apparently caused the resistance in the wire to increase and thus caused the error message. They told me they Ohm'd every related wire several times and couldn't find it. I assume they could only find the bad wire when the conditions were right to cause the resistance to increase enough to set off the error. Every week when I called them they told me that they couldn't find it yet and how difficult it was. I'm glad they stuck with it and finally were able to fix it.
     
  9. Tombukt2

    Tombukt2 Senior Member

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    Yeah in that case since I have unlimited amount of these things personally I would have had to put that one aside and come back to it maybe someday but yeah those wires that run in the transmission or many and they run in that oil and some of the external covers and plugs where you can unplug these things and pull them out the wires don't look like they're a good thing but they're working so I leave them alone I mean at some point Toyota had problems with making wire covering with soy in it that rodents love to eat so I can't imagine what might have happened to the wire inside the transmissions and other places but hey it's a process.
     
  10. Tombukt2

    Tombukt2 Senior Member

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    Now I'm wondering if that resolver wiring issue could be caused by incorrect or seriously broken down transmission fluid? That is interesting I believe that wiring runs in the transmission fluid or it sees the transmission fluid or something along those lines when I was poking around in my '05 parts car I had disconnected some of those covers on the transaxle to look and see how some of this wiring was connected and worked and I do believe I have to go back out there and look but I think those wires under those covers plug into gray colored plugs that I think are covered in transmission fluid or splash or something along those lines and having the improper transmission fluid that isn't copesthetic with wiring and whatnot I wonder if that would help move this problem along.
     
  11. ChapmanF

    ChapmanF Senior Member

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    "Shift control actuator assembly", yeah. It contains a rotor that moves the parking pawl in and out, and a "rotation angle sensor" that reports the position of the rotor so the ECU that drives it can drive the three phases with the right timing.

    I suspect the term 'resolver' here can lead to some confusion. There are two 'resolver's inside the transmission, one each for MG1 and MG2. Those serve the same purpose for MG1 and MG2 that the shift control actuator's "rotation angle sensor" serves for it. The wiring for those resolvers runs inside the transmission.

    I don't think any wiring for the shift control actuator's rotation angle sensor runs inside the transmission at all. It's all inside that little actuator assembly.

    Toyota doesn't call the angle sensor in that actuator a 'resolver', even though the basic purpose is the same. A resolver is one way of tracking the angle of a spinning rotor, and it's the way Toyota does it for MG1 and MG2. The angle sensor in the shift control actuator uses Hall-effect sensors to accomplish the same thing.

    Because the shift control actuator uses Hall ICs for that, I can kind of imagine how they could have had the magic smoke let out while somebody was working on stuff. (It would be harder to imagine 'frying' the MG1 and MG2 resolvers, as those are just wire coils; the magic smoke for those is all in the ECU they connect to.)