Jerkiness while sitting in park with parking brake on, anyone else experience this?

Is it the ICE starting up? On a cold car, the engine will start up a few seconds after you turn the power on, even if you are not moving or in Drive.

 

I have noticed the same thing. If you are sitting with the car in park when the ICE starts up it feels like the car wants to go. It feels like it is straining against the transmission interlock. If you have a foot on the ground and the parking brake off you can really feel it move around.

Regards,
NoSpam

 

I had similar questions before I got used to the car's behavior. If you search for "shake" or "shudder" you will find numerous posts on this topic. It seems to be more pronounced when you first start up from a cold engine. I noticed it also more on the first engine shut-down. At first I thought there was a problem but later learned that it is one of the little quirks of how the car operates. I can't find the post but I remember reading something about the engine always being in drive - or something similar. Come on guys; one of you gurus will be able to explain better than I can.

 

<div class='quotetop'>QUOTE(Neicy @ Jul 20 2007, 07:26 PM) [snapback]482518[/snapback]</div>

Yeah, I've got the same thing going.

 

<div class='quotetop'>QUOTE(NoSpam @ Jul 20 2007, 06:01 PM) [snapback]482507[/snapback]</div>

Me too, happens only occasionally when I'm still in park, car moves forward and stops.

 

This happened twice now, once when I was driving and yesterday when my wife was driving. The car is in Park....you start the car and let off the brake. A few seconds later, the ICE kicks in for the first time and the car moves forward an inch or two. What's up with that?? When it happend to me, I thought the car slipped out of park.

Does anyone have an explanation on why this occassionally happens?? Should the dealer look at this??

Thanks.

 

I have a thoery, but may be way off:

When a cold engine idles, it may idle rough due to the fact the air/fuel mixture is way rich until it warms up. The Prius engine electronics operates MG1 at a speed commensurate with engine rpm, desired wheel speed, and desired wheel torque. My guess is when the engine runs rough, the electronics has quite a job trying to adjust MG1 speed to keep the wheel speed and torque at zero. The result of this 'chase' scenario is the jerkiness you encounter. When you put the car in Drive, MG1 will compensate for engine rpm to provide drive torque and speed to the wheels. Since the car will likely be accelerating at this point, you will not notice the jerkiness because MG1's speed is constantly changing.

I notice a very similar symptom when I let off the pedal to transition from an acceleration mode to a cruise mode and feel the car jerk slightly.

I do not know, maybe I missed the boat on this one.

 

Pretty simple - don't take off the parking brake until you intend to move off.

Here in the UK, we all learn to drive on manual transmissions*. If you take your foot off the clutch with the car in gear, it either leaps forward, stalls, or leaps forward then stalls. If you take the parking brake (handbrake) off with the car out of gear it is virtually guaranteed to roll. The hill-start procedure on a manual is: put clutch down, shift into first. Apply power to around 2,000 revs with right foot, bring clutch to bite point, until the car strains against the handbrake. Release handbrake - car moves off smoothly. Never ever take the handbrake off without knowing the car is going to move in the direction you want.

The dealer suggested simply putting the Prius in Park - transmission park - when stopping temporarily. While this will hold the car, it puts stress on the transmission, which is an expensive component, rather than on the brake pads, which are relatively cheap, easy-to-replace components.

When stopping for a light, I now come to a halt, apply the parking brake while shifting into Neutral, let the parking brake take the strain, then press the Park button for transmission park. (The car cannot regenerate in Neutral.) To move off, press the brake pedal to prevent the car rolling, shift into D, release the parking brake with the left foot and move the right to the accelerator to pull away. Creep holds the car even on fairly steep hills, but you can press the parking brake down to release the ratchet and hold your foot there, still keeping the brake applied, while applying power with the right, until you feel the car has enough forward power to move off without rolling back. Then release the left foot to move off.

* OK, you're allowed to learn on an automatic. But if you pass your driving test on an automatic, you're then not legally allowed to drive a manual until you pass a test on a manual. The vast majority of cars here are manuals.

 

Some people say I have a lot of jerkiness, I guess this post is evidence of that.

 

I think your theory is on the money. You don't have to be in Park to experience the jerk, it happens while in Drive too, for example waiting for a traffic light. I also experience the slight jerk changing from acceleration to cruise though my wife is unaware of it happening.

 

You do that at every light merely to avoid holding the brake pedal?

 

This is a lot like the debates we used to have about holding in the clutch at a traffic light. One side said it was the correct thing to do because then you were ready to move in case of an emergency. The other side said you should shift into neutral to save the wear on the clutch throw-out bearing. Both arguments had merit, but each was silly in its own way.

With the Prius, if I'm sitting for a long period I will hit park. If I'm just waiting for a light, I keep my foot on the brake. I only use the parking brake for parking, and then only on hills.

As for driving a manual transmission, I grew up driving manuals on hills, and I never used the parking brake for getting started. Most of the cars in those days had foot pedal parking brakes, as does the Prius, and they weren't convenient for hill starting. Any good driver could easily engage the clutch while moving his foot from the brake to the accelerator, all without rolling back. It isn't that hard to do.

Tom

 

The jerk you are felling in park is the engine powering the battery.
When you turn the car on to "ready"\
Switch to the info screen "energy"
You will see the engine feeding the battery- the jerk comes from the engine engaging the electric motor to generate this power- don't worry it is normal and inconsistent as the computer decides when the car needs a lil chargin:rockon: