Gen4 no power- how can you put in neutral?

Discussion in 'Prime Technical Discussion' started by PixelRogue, Jun 13, 2025 at 1:09 PM.

  1. ChapmanF

    ChapmanF Senior Member

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    That's fine; the documentation from when I conducted that experiment is what you saw me post in February (linked upthread), which either is or isn't enough to satisfy you, and if it isn't, well, that's exactly why experiment results get reported along with the step-by-step of how anyone else can reproduce the experiment.

    There are some experiments that take a lot of time or prep or special equipment to conduct; this one is dead easy. Matter of minutes. The connector A23 mentioned in my instructions is correct for gen 3 (accessed by easy removal of the glove box); anyone reproducing the experiment in a different generation will need to spend a moment with the wiring diagram to find the corresponding connector for their generation, and that'll be the hardest part of the whole thing.

    The main reason we haven't seen some other PriusChat members already reproduce it might be that they haven't seen a need, not generally suspecting me of faking experiment results. But if you do, that's totally fine; the whole point of including the repro instructions with the results is to make it clear that anyone wishing to check my work for any reason is cheerfully invited to do so.

    Under the circumstances, I'd be happy if a few more members felt like reproducing it and reporting their own results. That still may not satisfy you personally, given your past history of even rejecting independent, corroborating reports from multiple members on another topic. Nevertheless, it would be of service to others reading this thread, who right now have little more to go on than whether they think you or I sound more convincing.



    Edit: strictly speaking, the experiment that I reported in February involved first unplugging the Park actuator and then powering off the car while already rolling (long-pressing the power button to force off).

    I spoke upthread of another approach, unplugging the Park actuator and then immediately powering the car off while stationary, then just rolling the powered-off car. I did it that way, too, around the same time in February, but might not have reported it then. Anyone wanting to reproduce the experiment could use either approach, or both.

    If you start with the car stationary and powered off in neutral, and then push to get it rolling, you'll notice your first push has to be a little extra hard. As outlined upthread in post #12, you could use the length and force of that extra starting push as a rough way to estimate the value of the capacitor circled in green.

    [​IMG]

    Doing that (and then comparing the estimate to the cap's labeled value) would be a fun addition to the experiment, which I might return to someday, time permitting.
     
    #21 ChapmanF, Jun 16, 2025 at 9:26 AM
    Last edited: Jun 16, 2025 at 9:43 AM
  2. Paul Gregory

    Paul Gregory Senior Member

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    It's just not worth it.
    Seeya.
     
  3. PixelRogue

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    Truly appreciate the details. Thank you.
     
  4. PixelRogue

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    I had a booster, tow driver had a jump pack and cables. We were stuck and am thankful the driver thought to trace it back to a loose connection. Now paranoid of ever breaking down w/o that requires a tow.
     
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  5. ChapmanF

    ChapmanF Senior Member

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    The well-prepared tow driver usually shows up with options in case a car can't be gotten out of Park.
     
  6. Paul Gregory

    Paul Gregory Senior Member

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    That might allow the shifter to go into neutral, but the car will not safely coast in neutral.
    The car can be towed for short distances at low speed when the car is in READY mode and operating normally.
    The approved way to tow a Prius is either on a flatbed or with dollies under the drive wheels.
     
  7. ChapmanF

    ChapmanF Senior Member

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    Towing with all wheels on the ground falls under the "Emergency towing procedure" in the owners' manual. That can be found on page 666 of a US 2022 (gen 4) owners' manual, or page 552 of a US 2023 (gen 5) manual, and presumably nearby in other editions.

    For both gen 4 and gen 5, the recommendation is for short distances and speeds under 18 mph (30 km/h).

    Both versions instruct you to "start the hybrid system" (go READY) if the car will, or if it won't, to go to IG-ON instead (two power-button pushes, no foot on brake). (As already covered in this thread, you need to get at least to IG-ON for the parking pawl to retract.)

    Both versions explain that if you tow in IG-ON rather than READY, you'll be doing without braking and steering assist. As for how easily the car can be pulled or pushed, there is no difference, as there is no need to have the hybrid system on for the car to roll in neutral.

    If there's any doubt about the 12-volt battery supplying IG-ON power for the full length of your tow (or, say, you have only used a small jump pack to get to IG-ON long enough to retract the parking pawl), unplugging the connector to the parking pawl motor after shifting to neutral will allow powering off without returning to Park. The car rolls just the same.

    I made some distinctions between gen 4 and gen 5 in this post because there are some differences in how the transmissions are lubricated. I'm relying on KMO's post here for those details.

    From KMO's notes, gen 4 Prime includes an electric oil pump for use in long stretches of EV driving. If there is no power, of course that pump will not run. Gen 4 still does have sling lubrication also, like the earlier gens, so oil will be circulated that way in any case.

    Gen 5 apparently has no more sling lubrication, but adds a mechanical oil pump driven by the output (which will therefore be pumping when the car is towed, power or not). KMO notes there are some control valves that select between the input-driven or the output-driven pump, but the notes don't say if those valves are electrically operated, or which selection is their rest position without power.

    With either design, the lubrication is probably going to be adequate for the short distances and low speeds that the manual recommends.
     
  8. Paul Gregory

    Paul Gregory Senior Member

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    I'm skeptical that you were able to disable the parking lock while the car was off.
    When I asked for evidence, you deflected.
     
  9. ChapmanF

    ChapmanF Senior Member

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    So you are skeptical of a claim made by whom? Are you saying that I have ever claimed I disabled the parking lock while the car was off? If so, please link to any post where I claimed that.

    Please identify (a) the post in which you asked me for evidence of that, and (b) the post in which I deflected. Please be specific.


    Are you perhaps thinking of the posts where I have described shifting out of Park while the car is ON, then unplugging the Park actuator motor, then turning the car OFF, leaving the car not in Park? Yes, I have done that, and made posts explaining how to do it. It is easy to do.