2001 Prius Engine Turning Over While Sitting At Light

No ideas, never heard of that happening.

 

So is there any reason you cannot open the hood in D when you "feel" this happening and go look at the serp belt to see if it is turning?

Maybe you have defroster on, maybe it is the servo in the steering wheel or the electric steering making noise.

 

Can you get a Prius friendly OBD scanner and actually see the ICE rpm?

There are a lot of electric motors in our cars and would not take much to 'sound like' what you are describing.

Bob Wilson

 

that behaviour sounds familiar to me. What I and also several other Prius drivers here in the german community discussed some time ago is an occasional "turning" of the ICE - we are talking about a half or up to one and a half turns only. Since the car is standing, it must be MG1 which is responsible for that.
It was concluded that the HV-ECU commands MG1 to push the pistons in an optimal position to provide a smooth start, when the ICE is needed for acceleration. Since the ICE can be stopped in any crankshaft position it is very likely that none of the pistons is in an optimal state for an immediate combustion.

Btw: this behaviour is not shown in the first 10 to 15 seconds after stopping. But after that, it can be felt sometimes. In my case it only occures 1 to 2 times a week.

Anyone who can confirm that?

Bye, Eisbär

 

Ahhh, so to see it, we would need to look at MG1 rpm? Have you seen it in ICE rpm?

I need to check if there is an OBD readout of crank or cam position that would absolutely confirm it happening. That I haven't 'sensed' it only means this observer has yet to pickup the clue(s). But I would be happier to see some empirical data.

BTW, the reason I mentioned motors is I have heard various 'brake' system noises . . . or what I assumed were the brakes.

Bob Wilson

 

I'm not sure this makes sense. If the ICE is required, it is engaged with a dampening disc and hooked directly to MG1 which is in the thousands of rpm, the ICE is started by spinning over 500 rpm, so how would it even matter where the piston start at. It wouldn't start easier with piston at TDC... or middle or anywhere, when the electric motor is spinning the ICE over 500 rpm.. why would the starting position matter?

I'm not sure that the ECU or MG1 has such fine motor control when you are driving and ICE shuts off where it has the luxury to be making micro adjustments like moving the ICE by 5% of one revolution..

 

I agree with "joedirte" as MG1 has a tremendous amount of power and brings the ICE online within 250 ms (near the limit of OBD instrumentation.) Now I do know there is a brief, counter-torque when the ICE is stopped to prevent a final 'shudder.' The protocol is:

• exit to level road above 42 mph with fully warmed ICE running
• shift into "N" while above 42 mph
• when speed drops below 42 mph, briefly shift into "D" and back to "N" -> engine shutters to a stop

If you have a Prius aware OBD scanner, monitor MG1 torque and do the following:

• exit to level road above 42 mph with fully warmed ICE running
• shift into "N" while above 42 mph
• when speed drops below 42 mph, shift into "D" and monitor MG1 torque as engine stops

I've seen other reports of a late 'positioning' of the ICE but I've not observed it with instrumentation . . . but I wasn't looking for it either. As I mentioned, I've heard brake system noises but nothing that I could associate with a late, ICE rotation.

Thanks,
Bob Wilson