21 Prime Limited creeping forward in every gear?

Discussion in 'Prime Care, Maintenance and Troubleshooting' started by stomish, Oct 11, 2021.

  1. stomish

    stomish New Member

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    Has anyone else had this problem?

    Went to run in a store yesterday in my 21 Prime, hit park and when I let off the brake, the car creeped forward as if it was in drive. Baffled, I looked down to confirm I had actually pressed the button and I had, it was lighting up. Pressed it a few more times for good measure, same thing. Still creeped forward, almost making me hit the pole in front of me. Put it in reverse, same thing, creeps forward, albeit a bit slower. I was able to overcome the creeping forward with throttle when in reverse, but it still creeped forward when I let off the gas. In neutral, it also creeped forward. The only way for me to stop this was shutting the car off. The car hasn’t done this problem since, but it has me extremely worried, made a dealer appointment to see if there are any hidden codes/if they can replicate the issue. To me, it seems as if MG1 and MG2 had a communication problem and were both doing their own thing.
     
  2. bisco

    bisco cookie crumbler

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    were you on a slope?
     
  3. stomish

    stomish New Member

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    Yes, but an uphill slope, so if anything the car should've rolled backwards, not crept forwards.
     
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  4. bisco

    bisco cookie crumbler

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    ya, that is very strange. i don't ever recall reading about it
     
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  5. ChapmanF

    ChapmanF Senior Member

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    There are very peculiar details in this story.

    In Park, for the car to "creep forward" more than a couple inches ought to be impossible. It may "creep" (or more likely roll downslope) but be stopped with a bonk by the parking pawl.

    The transmission control ECU is not at all casual about moving the pawl into and out of position, and knowing exactly which position the pawl is in at all times. If it loses track, or can't move the pawl when it intends to, it will generally get your attention by blinking the P button light and showing a P position malfunction message on the display and showing the master warning light and setting trouble codes with freeze frame data and possibly buzzing at you or powering down the car. (I'm taking this from the Gen 3 repair manual, but I don't expect it to be hugely different for Gen 4.)

    So for you to really see none of that and the car be able to "creep forward" any meaningful distance in Park, the number of things simultaneously wrong seem to me pretty inconceivable (whether or not that word means what I think it means).

    Alternatively, there's a good chance there are codes and freeze frame data stored that will help make sense of the story.
     
  6. Mendel Leisk

    Mendel Leisk Sand Pounder

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    Parking pawl is supposed to engage in Park; car should not move, apart from an inch or so rocking. Either pawl’s not engaging, or Park button is not working? Have dealership look it over? With a 21 it shouldn’t cost.
     
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  7. vvillovv

    vvillovv Senior Member

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    If I'd experienced that one time, I'd write down for my own records (like you posted above, adding) mileage, where and how I drove before it happened - anything else strange noticed on that previous drive, where it happened - the exact spot, how I had the dash screens setup and was anything (like the radio/CD on) at the time.... Going out on a limb with a wild guess after reading above, almost like it might be related to Hill Stop misbehaving, But in Park Reverse and crawling uphill !!!! Big Question Marks there??? and super strange !

    Like @bisco said above, I have read about anyone else noticing that either, which was where I logged in and started to write, than I saw Mendals comment but missed Chaps post. Than I went back to the OP and noticed the sig. (now curious bout the mods). Than I read Chaps post.

    I wish @Elektroingenieur and a few others I follow were still posting once in a while. They can't all be driving Tesla now, can they?
     
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  8. dig4dirt

    dig4dirt MoonGlow

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  9. bisco

    bisco cookie crumbler

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    my prius can roll 6-8" in park, but not against the slope
     
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  10. stomish

    stomish New Member

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    Exactly, it was extremely bizarre. No warning lights, no blinking P button, etc. If I let off the brake while the car was in "park" I would've creeped forward and hit the pole in front of me. Fingers crossed the freeze frame data will show some kind of miscommunication/make sense of it all.
     
  11. bisco

    bisco cookie crumbler

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    i always blame it on being 66 years old...
     
  12. stomish

    stomish New Member

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    Definitely took note of everything going on at the time as well as which actions I took. Seems like a strange miscommunication between motors/with the transmission. The only thing I've noticed that had ever been remotely off about the car is a couple times when transitioning from ICE to electric motor and back it felt a little lurchy, but I wrote it off to being a coincidence/me not being used to driving a Prius yet (happened within the first 1-2k miles of ownership, maybe two or three times total).
     
  13. stomish

    stomish New Member

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    +to add to all of this, I do have it captured on dashcam, front and rear. I'm going to pull the footage when I get home, as I just remembered you'll probably be able to see the reverse lights being on while the car creeps forward.
     
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  14. vvillovv

    vvillovv Senior Member

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    Yes, that rough transition has been noticed by more than just a few, but not everyone. I've noticed it too, and I've noticed it like you, mostly only when the car is new and the ICE hasn't been run very often yet. There are a few combinations that will make that transition more noticeable I've recognized with our Prime. Most notably, cold temps (freezing) coupled with steep incline and 0 EV range. Reversing those three variable has worked in reducing the rough Motor/Engine transition when the car was new, for me. As always YMMV
    of yeah easing up of the Go Pedal when the ICE starts has helped me reduce the rough transition too. Not easy if going uphill....

    Primes are fairly complex machines, and Prime drivers have noticed some strange behaviors. Some have been figured out and one of two are still mostly mysteries.
    Keep in mind that most/all hybrids use history data (about previous driving). That can make big differences in the description of the cars behavior by different drivers that drive with different conditions, like weather (all inclusive), geography, traffic, speeds, etc. ;)
     
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  15. Neicy

    Neicy Member

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    I have made a habit for years to engage the emergency brake before pressing park to take some of the pressure off the parking pawl. It never budges. I think I started doing that around the time the "unintended acceleration" issue was going around. So maybe I'll try not doing it for a while just to see what happens. I had not heard of this issue until I read this post though. All my Prii have always rocked a bit when put in park without the emergency brake engaged but never actually moved a perceivable distance. Scary.
     
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  16. rdgrimes

    rdgrimes Senior Member

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    Doesn't the '21 have an automatic electric parking brake?
     
  17. stomish

    stomish New Member

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    Nope, still foot brake


    iPhone ?
     
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  18. stomish

    stomish New Member

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    Update on this, went to the dealer, showed them dashcam footage, they ran full scans and were unable to recreate the issue. Hopefully it was just a fluke and doesn't happen again!
     
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  19. ChapmanF

    ChapmanF Senior Member

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    Are you able to post the video here?

    The creeping forward in Park part is what I would be most interested in seeing.
     
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