Why such low torque?

Discussion in 'Gen 3 Prius Technical Discussion' started by Paul Gregory, Jun 27, 2025 at 8:23 AM.

  1. Paul Gregory

    Paul Gregory Senior Member

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    My Gen 3 would get stuck so easily, too weak to pull itself out of a small gutter in the doorway to a shop. I had parked it there to do some work, and the rear wheels had fallen into a small gutter (for the door track) a few inches wide. I could not get the car out of it, and had to be towed. I thought it should have had the power for that, easily. Why so weak on start-up?
     
  2. Tombukt2

    Tombukt2 Senior Member

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    Put the car up dead.. do not know . Going reverse ?
     
  3. Paul Gregory

    Paul Gregory Senior Member

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    The car was running perfectly fine otherwise. I imagine it would be unable to pull itself up a ramp.
    Annoying and puzzling.
     
  4. Mendel Leisk

    Mendel Leisk Senior Member

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    When was this; do you still have it? In my personal experience, it turned out to be “user error”: parking brake left on.
     
  5. ChapmanF

    ChapmanF Senior Member

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    Were you trying to reverse out of that position, or drive forward?

    Reverse is more of a challenging situation for the car, because it doesn't get to use engine power to supplement the battery: while the engine can spin MG1 to generate more electrical power to send to MG2 in reverse, at the same time 78/108 of the engine's torque would be passed through the transmission in the forward direction, working at cross purposes. So the car generally stops the engine when you need any significant reverse power. If the engine ever is running in reverse, it's generally idling, and contributing no significant power to reversing.

    So your available power in reverse is limited by what's available from the battery. The power management control ECU computes a "Discharge Control Value" which is the maximum it will demand from the battery at a given moment, never more than 30 kW in gen 3 and at times much less, depending on things like the battery temperature and its estimated condition. Divide that discharge control value by the nominal battery voltage and you get the maximum current available to make MG2 torque for you in reverse.

    If I ever needed to reverse up a long hill, I expect I would have to stop along the way, wait for the engine to recharge the battery and possibly for the battery to cool, then continue reversing.

    Driving forward is a simpler proposition, and the engine can kick in to help. If you were trying to drive forward then I can't say what the trouble was.
     
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  6. Paul Gregory

    Paul Gregory Senior Member

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    I know you don't mean to insult me, but no, that's not it.
    It simply didn't have the power to pull itself out of a small groove.
    I sold my Gen 3 last year, and no faults were ever found.
     
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  7. ChapmanF

    ChapmanF Senior Member

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  8. Tombukt2

    Tombukt2 Senior Member

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    That's hysterical my '09 with a near dead hybrid battery that's driven on rae occasions now will. Pull itself up a truck ramp at a commercial. Loading area . I pull up in they're to load up stuff in shade into the Prius gen2 . This is a slippery piece of steel ramp tires sliding etc squeaking going up.
     
  9. Paul Gregory

    Paul Gregory Senior Member

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    My car was still fairly new and fully checked out as normal.
    Was this a quirk of the Gen 3 in some way?
    It seemed to be performing perfectly normally otherwise.
     
  10. ChapmanF

    ChapmanF Senior Member

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    Are you ever going to answer whether you were reversing or driving forward?
     
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  11. Brian1954

    Brian1954 Senior Member

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    Paul may have you blocked and is not seeing your posts.
     
  12. bisco

    bisco cookie crumbler

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    i never had any trouble with mine, but i can't really understand what a 'small gutter in the doorway to a shop' is
     
  13. ChapmanF

    ChapmanF Senior Member

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    Perhaps ... though in another thread also this morning he replied within eight minutes.

    Also, I was not the first or only poster in this thread to ask whether he was reversing or driving forward.
     
  14. Paul Gregory

    Paul Gregory Senior Member

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    I had backed up to a shop door, and my rear wheels settled into a door track, which was a channel about 2" wide and about an inch deep. I never imagined I wouldn't have the power to drive out of that.
     
  15. ChapmanF

    ChapmanF Senior Member

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    So having backed up to the shop door, are you saying that your attempt to drive away was forward?