P-button, then Power off, vs just Power Off

Are you parking on a slope? Is your transmission oil too thick?

 

The only time I ever hit the Park button is if I want to sit in the car without turning it off. Turing off the car automatically puts it in Park.

If you stop the car, your foot will be on the brake when you turn it off. If you're on level ground, the car will just sit there when you lift your foot off the brake pedal. When you start up the ICE, it will apply a little torque to the drive train. That will try to turn the transaxle. If the Park pawl is engaged in its slot, nothing happens. If it's not, the car will roll till the pawl drops into a. slot.

If you stop and put the car in park, then lift your foot off the brake before turning off the car, the pawl will engage right then rather than later. Looks like this:


(From post #2 here: Prime rolls when put in park even in small incline | PriusChat)

 

People here told me that something was wrong with my car and take it to the dealership when I describe the slight jerk or tug on cold soak start up like yours.

 

I've mostly forgotten that P button even exists, virtually always shut down with right foot on brake, push down parking brake pedal with left foot, release both. Haven't noticed a kick on start up.

Do you know if the transaxle fluid was ever changed? What was used?

 

OK, there is a difference.

When you hit P, the car's electrical system powers an electric motor into a locked position.

When you turn off the car, the 12 volt battery powers an electric motor into a locked position. If it is dead enough, you get a P-lock Malfunction, which contains the bad advice that it might be a transmission issue.

If you are noticing a subtle difference, I would check the 12 volt battery, it may be weak.

 

Sooooo! What happens when you accidently put the car on park with the power button than the park button? It is at a complete stop with the foot on the breaks. Does this ruin your car? My maintenance light came up, then again I am also due for an oil change. I also have a Savy device that I use to read my car. After parking with the power button, my Savy device was not able to read the gas mileage.

Has anyone experience the park via power button before? Any issues?

 

if you press the power button first, the parking pawl has already been engaged, and the park button is deactivated

 

As far as I know, the car literally doesn't care. It is programmed for pushing the power button while not in Park to mean "act like I pushed Park and then the power button."

Post #6 suggests that there is a difference, and the car drops out the DC/DC converter in that case before shifting to Park. That would be interesting if true, but I don't know that it is. A simultaneous scope trace of the converter output and the park status would be able to answer that question.

 

With my experience, when I turned off my power button instead of the park button, my entire car turned off. The summary of the trip doesn't show up, the screen turns black. But the park button immediately lighted up. So in theory, the power button can act as a park button. When I turned it back on (maintenance sign came on but it's probably because I need an oil change soon) I went for a longer drive and now my Savy device and car is reading the MPG again.

 

Exactly—it's not just theory, it's documented in the owners' manual. The car is programmed for Park when you power off, if you have not pressed Park already.

Toyota's designers might not have foreseen everything your add-on Savy device might or might not do. But anyway, the car isn't going to be damaged, or care which way you park and power off.

 

PARK first before turning off. You're putting too much load on your battery by using the power button as a park-shortcut. Otherwise you'll risk getting the P-lock malfunction error message and yer stuck!

 

15 years of pushing the Toyota Power button instead of Park first. No obvious problems. However when you buy a Honda with Push Button start stop, the result is not as good. The Honda will stay in Drive and you can roll. So they provide an electric e-brake that optionally engages on engine shutdown.

 

The reason for the "jerk' is as jerrymildred said. It's a byproduct of the way the transmission works. To elaborate a bit, the planetary gear set at the "heart" of the Prius transmission is (somewhat like a differential) a three-shaft affair which maintains the torque on each of the shafts at a fixed ratio relative to the torque on both the other two (ignoring minor effects of friction). Therefore, you can't change the torque on one without changing torque on the others. In the case of a Prius transmission, one of the three shafts is connected to the engine crankshaft, one (though other gears) to the wheels, and one to a motor-generator commonly designated MG1. When MG1 sends torque through the planetary gears to the engine to start it, backward torque must go to the shaft associated with the wheels. That causes the car to jerk backward slightly, until the parking pawl (or brake) stops it.

Whether you do or don't use the Park button before the Power Off button should have no direct effect on the tendency of the car to jerk backward the next time you power up. Maybe there's some indirect correlation related to your habits or circumstances. The short backward lurch will be most conspicuous if you've parked on a slight downhill without using the parking brake, and if you release the brake pedal after you hit the power button, but before the engine starts..

 

No maybe about it. The maintenance light comes on briefly 4,500 miles after the last reset. If you don't reset it by 5,000 miles, it'll stay on. It simply means it's time to check the maintenance schedule and do what's indicated in that document. For a Gen 3, that's rotate the tires each 5k and change the oil each 10k plus whatever else might be on the list for that particular multiple of 5k miles.

 

This looks like the same claim made in post #6, namely that using the power button first causes the DC/DC converter to drop out immediately, then shifts to Park on battery power.

That would be interesting if true, but I don't know that it is. It's also possible that the car is programmed to treat power-off when not in Park as simply Park, then power-off. A simultaneous scope trace of the converter output and the park status would be able to answer that question.

 

Agreed. In fact, given the elegance of the engineering that created the Prius drive and control system, I'd be totally astonished if they did something so dumb as to program it to shut off the DC/DC converter before the car was finished with its shutdown chores. But aside from that, if running that little motor on the 12V w/o help from the converter is bad, then it's also bad to run the brake pump and turn on the dome lights before starting the car and running the emissions check after shutting it off.