Sudden movement

Yes, actually it has happened to me twice.. I spoke with a service advisor about it and of course he had never heard of anything like that before. He gave me the deer-in-headlight look like I was crazy.. And of course I cant get the car to repeat this glitch. Im going to be scheduling a service appointment to fix some rattles (front passenger seat) and squeaks (center speaker) and Im going to include this glitch in that repair. I figure if they cant find it.. at least I will start a documentation trail. I'll let you know how it goes. By the way, is yours a 2006 like mine?

Dean

 

Nope... but I know what you are talking about.

All automatics have a little play against the pin that locks the transmission but it's in the order of less than 5 millimeters.

Here's my guess what is really happening...

1- You drive up to a parking place and come to a full stop with your foot on the brake. It doesn't really matter if you are under gas engine or full electric power.

2 - You put the car in park and still have your foot on the brake.

3 - If under gas power, the engine shuts off. Regardless of motive power, your foot is still resting comfortably on the brake.

4 - Suddenly, the ICE kicks in and you even without thinking remove your foot from the brake.

5 - The Prius can roll a few millimeters (NOT a couple of inches though) until the transmission pin "locks." All cars do this, but it's really noticable on a Prius because a normal car keeps the transmission under torque until the engine is powered off. The Prius does not have a normal transmission. Heck... not much is "normal" in a Prius!

6 - You, startled at the rolling of the car to the transmission pin, quickly place your foot back on the brake (or NOT!) but it sure SEEMS like the car rolled all by itself and two inches, too!

THIS is CAN duplicated each and every time you stop the car. It drives my wife nuts if I don't take my foot off the brake and let the Prius settle before she jumps out of the car!

I welcome you to try the process for yourself.

 

Good guess-- but wrong!

I drove to the post office yesterday with my wife, left car in park and went in. When I came back she said the car scared her, the ice had started and the car moved a few inches.

 

nope.. not the senario i was talking about...

the first time this happened to me was the first night I brought the car home from the dealership. I spent maybe 30-45 mins parked inside the garage (door open of course!) with the car in PARK and the power button on (ready light displayed on dash) And the whole time my foot was no where near the break (after intially parking in the garage) I left the car in this state to keep the cabin warm while i was playing with all the controls and gadgets getting comfortable with the car. after a few mins the ICE cylcled on as usual and no discernable movement of the car was noticed... The ICE cycled off after recharging the battery and bringing the coolant up to temperature for cabin heat... several mins later the ICE cycled back on but this time the car LURCHED forward a good 6 inches (i know the difference between a couple of MM and a half a foot!) scared the bajesus out of me, thought i was going into the wall in the back of the garage. luckily it stopped rolling just as my foot was reaching for the break. It wasnt a jerking stop (like when an automatic transmission engages the locking pin) but more of a breaking type of stop. after I collected my stomach i double checked everything to make sure i was indeed in park which i was. I spent the next 15 mins trying to get the car to repeat the "LURCHING" but was unsuccesful.. The ICE would cycle on and and the car would hold its ground..

 

My car has done this (I've been spending way too much time in the garage with the car on, playing with all my new controls and settings). I assumed it was a function of the engine kicking in....just goes a couple inches....I haven't gone through any walls YET. I felt this was in the "normal" range and didn't worry about it.

 

Yup, happens to me from time to time, PARTICULARLY if the e-brake isn't fully engaged. What's causing it is the torque of the rotating starter/engine, in conjunction with actually "firing up" of the ICE. It sort of "jolts" on sometimes, I really think that it's just the way it is, as ICEs sometimes start slightly differently due to where precisely the valves are when it shuts down. Sometimes they're "aligned" better, and start smoothly, sometimes not... That's my theory on it...

 

As Priusham says it is a normal function of all automatic transmissions. The difference being that in 'normal' cars the engine is on and puts pressure on the pawl. In the Prius the engine is off and when it comes on it moves the car forward against the pawl. There is some small amount of play in the gears.

Put on the emergency brake when stopped and this will not happen.

 

I always try to use the parking brake first when parking, even before hitting Park. I don't like the car (any car) to strain the transmission when the brake could be keeping it still.

I HATE it when I get into my car after a service visit and feel it rock because the parking brake wasn't used...

 

If you put the car in park (engine on or off) without the emergancy brake and then try to rock the car foreward and back from outside, you will see the car has an inch or so of play in the drivetrain. It's the same as any other car with an automatic transmission. This is what you are experiencing when the ICE starts up in Park.

 

Another thought... in a normal auto tranny, the Park function is created by engaging a pawl in the flywheel (or more accurately a ring gear on the torgue converter). Since there are only so many teeth on the gear, there is a certain minimal engine rotation that may need to occur before the pawl fully engages.

The Prius uses a slightly different mechanism, but perhaps the "rotation quantization" effect is still there; i.e., the pawl/pin isn't fully engaged until the ICE and tranny gears are positioned just right for full engagement.

Now suppose you came to a stop with the ICE off. The ICE and gears may not be in just the "right" position for full Park engagement. Sitting in Ready, there is no movement... until the ICE starts, lets the car/tranny rotate just that little amount, the pawl fully engages, taking up any further drivetrain slack. This might amount to a couple of inches of car movement.

It would not repeat because now the pawl is already fully engaged, preventing the lurch. It might also explain why this is reported on level ground; on a hill the movement might cause full engagement, preventing this "limbo" pawl/gear engagment scenario.

 

What tootallrls and Headshop describe has been commented on before on other Prius boards. In fact, the conversation was similar to this. What priusham describes (excellently) is very common, but I don't think it can account for what seems to be a pretty uncommon problem. Only a handful have noted it, without a bunch of people chiming in, "yeah, me, too".

My reaction when I heard it was that the car(s) might not really have been in "park", but that wasn't known because it was on a level floor. Could they have really been in neutral?

To my knowledge, no one claiming the problem has ever duplicated it with a dealer, and no satisfactory explanation has been offered.

Rather than await its happening again, I'd be prudent and use the emergency, which I do by habit anyway. Still, that leaves you with a bit of a mystery.

 

I'm glad that other people have experienced this. I've had my used 2006 Prius for about 7 months. This always happens when I'm sitting in the car, IN PARK, and my foot is off the break. Sometimes the a/c is running, sometimes not. The car will suddenly jerk forward 3 to 6 inches; I haven't hit anything yet. This has happened to me dozens of times. This "quirk" seems dangerous and really unacceptable. Has Toyota put out anything on this? Any recall?

 

If you don't want the car to jerk forward when the gasoline engine starts, then set the foot-operated parking brake.

There is no recall.

 

Ditto that. When you are parking, set the parking brake. End of "problem".