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    AaronA Junior Member

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    My wife parked our 2007 Prius in the driveway tonight, which has a decent incline, but when I looked out the front window a half hour later the car had rolled into the street! She turned the power off before she got out of the car which should have automatically put it into park, and the car didn't move when she got out of the car. I'm going to bring it to the dealer tomorrow, but any ideas on what it could be? why the car would start rolling after it had been parked? Anyone had a similar problem? I've got it parked with the parking brake now, though it really shakes my trust in the car.
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    uart Senior Member

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    If you park on an incline you need to apply the park brake, that's what it's there for. Park is just a bit of extra insurance against it gradually slipping a little on the park brake, it's not a substitute for the park brake.

    Given it's a "decent incline" the best procedure is to

    1. With one foot firmly on the regular foot brake, apply the park brake very firmly with the other.

    2. Shift to "N"

    3. Remove your foot from the regular foot brake and make sure that it holds on the park brake alone. (The car may move a half inch or so while it takes up the load on the park brake).

    4. Assuming that it holds ok then shift to "P", or just power off.
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    cwerdna Senior Member

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    I always apply my parking brake since the Prius rolls/rocks quite a bit after Park compared to regular automatic cars.

    However, I'd consider the OP's problem a safety issue. I'd file a safety complaint with Home | Safercar -- National Highway Traffic Safety Administration (NHTSA). IIRC, I've heard of cars recalled for having problems w/rolling away when in Park.

    I'd file
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    AaronA Junior Member

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    We have parked many other cars in the driveway and never had any issues. This car has been parked for the past few weeks (it's new to us) and never had an issue. My assumption was that the Park button was exactly like putting any automatic car into Park which locks the transmission so the car can't move at all. Is it different in the Prius?

    The incline on the driveway is about 25 degrees or so, I can't imagine that would be enough to pull an automatic car out of park.
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    Rokeby Member

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    richard schumacher shortbus driver

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    The parking pawl must be broken. Get thee to a dealer ASAP. In future always use the parking brake.
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    uart Senior Member

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    :eek: 25 degrees is a huge gradient, almost 47%. Most driveways would be under 15% at the very maximum.

    You're probably over-estimating it, most people tend to do that. Other than doing some serious off road 4WD'ing you're not likely to ever drive a 47% gradient.
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    uart Senior Member

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    It can't pop out of engagement if the load exceeds some maximum value can it? Perhaps it's designed to do that rather than break off and stuff the transmission.

    One other thing to consider when relying on just the transmission park is that the parking pawl engages before the final drive differential. This means that it doesn't positively lock both wheels! If one wheel is on grass or something slippery (or very lightly loaded because of some unusual angle or loading) then the other wheel CAN roll, provided that the first wheel can slip and spin backwards. This is true of most transmission locks and is something that most people overlook.

    I would never rely on the parking pawl over the parking brake on anything even close to a decent incline.
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    seilerts Battery Curmudgeon

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    The parking pawl relies on the 12V battery to set the pin. This is a trick that I use to move inop cars around: put it in neutral, disconnect the 12V, and then power off. Particularly if the headlights were on too, there may not have been enough oomph in the battery to operate the pawl.

    Powering off without pushing the P button is a very poor practice, because there is no way of knowing that the pawl has engaged.
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    qbee42 My other car is a boat

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    The parking pawl on the Prius is very robust. It is electrically actuated, so this sort of problem could be caused by a blown fuse or failed actuator. Likewise there could be a mechanical problem with the pawl.

    All that aside, the most common cause of this sort of problem is leaving the car running.

    Tom
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    AaronA Junior Member

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    Sorry about that. It's not a real steep driveway, but it's not flat. It's steep enough to be slippery when it snows but still be drivable. It's also been fine parking my Volvo and two other Toyota Corollas (my landlord's and my old one) with no need for the parking brake. My landlord has lived here 15 years and she has never used her parking brake, so this was all the more unusual.

    As for the post about putting it in park before shutting off the power: The car puts itself into park before shutting down, and the parking pawl has certainly engaged when I've done that in the past. My impression from reading other posts is that it's really difficult to get the car to shut off while in Neutral (it required pulling relays or something like that). So would it make a difference if I put it in Park first or just shut it down?

    I brought the car to the dealer this morning and I'll post when I hear back. I couldn't duplicate the problem this morning, so I'm hoping they can!
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    uart Senior Member

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    I'm not sure, but I think Seilerts point about this was that if the 12V battery was failing then it may not complete the shift into park when you turn it off. It might begin winding in the pawl but not complete the operation. It's never happened to me personally but I think he's saying if the car's still on you'll at least you'll get an error message if it fails to engage park.
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    AaronA Junior Member

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    Interesting idea, I don't think I fully understood the first post. Does the power switch shut off the 12v battery or just put it to sleep? I assumed that it has a shut down sequence that includes putting the car in park, but does the power switch act as a 'hard' shut off switch that just kills the car?

    If the shop can't find anything, I'll put a load tester on the 12v battery and see how that is functioning.
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    AaronA Junior Member

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    My wife always puts the key into the dash (I leave it in my pocket because I think it is so cool that the car can do that :)). The slot in the dash locks the key in place until the power is shut off, so she had definitely shut the car off, though I thought the same thing at first...

    When I get the car back, I'll put it in drive, pull into the driveway, take my foot off the pedals and see what happens. Maybe I can duplicate the problem that way.
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    qbee42 My other car is a boat

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    The power-down sequence does put the Prius in park before powering down. The issue is whether that action occurs before the DC to DC converter goes off-line.

    When powered down, the 12V battery remains connected and powers any 12V devices. When powered up, the DC to DC converter powers the 12V bus from the HV system while the 12V battery charges from the 12V bus.

    A failing 12V battery can produce all sorts of quirky problems with the Prius. It's worth checking.

    Tom
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    Eoin Active Member

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    I always apply the parking brake before leaving the car, even on level ground and for just a few minutes. I don't like the way it rolls without the brake.It's a good habit to get into.Cars have parking brakes for a reason.
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    AaronA Junior Member

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    Just got the car back from the dealer. They found.... Nothing! They could not duplicate the problem. I asked them about the 12v battery and they checked it and said it's slightly low, but good (not sure how they tested it).

    I will put it in park, listen for the pawl to engage, then hit power, then use the parking brake on the driveway or any incline.

    Any other ideas on where to go from here?
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    uart Senior Member

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    qbee42 My other car is a boat

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    Generally this is true, but if the fob is not inserted all the way it can be removed while the car is running.

    Tom
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    richard schumacher shortbus driver

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    So the pawl is not broken. In that case:
    - Test the 12V battery yourself. One can't be sure how the dealer did it, and a pass-fail tester can be wrong about Prius batteries.
    - Your wife didn't actually shut off the car. Does she lock it every time she leaves it?
    And, of course,
    - Set the parking brake every time you park.

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