'07 prius shudders while at stoplight (and other ?s)

<div class='quotetop'>QUOTE(gonegreen @ Mar 22 2007, 11:15 AM) [snapback]410214[/snapback]</div>

I have the same issue with Two 2004 Prius. It feels like either the electric motor or gas engine are still trying to drive the vehicle forward or like the transmission is engaging and disengaging while you're stopped at the light.

Does anyone else know if this is worth being concerned about or just normal behavior?
Thanks in advance for any information.

 

It's just the engine shutting off. It's most noticable during the warm up period just after starting the car. Once the engine is warmed up, it shuts off much smoother. Also, once the engine is warmed up, it usually shuts off as you are decelerating for the stop light, but when the engine is cold, it waits a couple of seconds after you stop before it shuts off.

 

I find that when I am at a cold stop, the shuddering is usually because (I assume) the HSD can't figure out whether or not it wants to turn back on.

 

<_< Here's an idea...

You may be exerting a little pressure on the accellerator pedal and/or not pressing the brake {not break!} pedal hard enough. If you will switch the MFD to the "Energy Monitor" {that displays arrows showing the power flow} and pull to a stop you might see moving arrows from the BATTERY to the WHEELS, indicating that you don't have adequate pressure on the brake pedal. This simulates an ordinary automatic transmission's action to prevent drifting back as on a hill. The Prius electric motor does the same thing if the brakes aren't sufficiently engaged.

If you have your foot resting on the accellerator pedal, even with slight pressure, the electric motor will try to engage resulting in little 'jerks.'

Your Prius is unique in many ways... this is one of them.

ENJOY YOUR PRIUS

 

I don't believe the HSD "can't decide". The Prius is so well-designed, I don't believe that there is not sufficient hysteresis built in that the computer sticks with its decision once it is made.

The thing that explains the shudder (and this applies to the question of the car moving slightly as it starts) is that the geartrain on a Prius is NEVER "disconnected" in the same sense as a clutch. The engine, wheels/electric motor, and starter/generator are all connected to each other via a power split device. In order to send power from the engine to the wheels, the car must take power out of the generator. In order for the starter to turn the engine, the motor must hold the wheels in place.

All this required perfect balance and is most noticable if you are not moving. Thus, the engine shutting down or starting when you are not moving, and especially if you are not holding the brake down is noticable as a slight motion.

Another odd thing that happens sometimes when you stop is that the engine will shut down, but the starter motor will actually keep it turning. I assume this is to run the A/C. My experience with this mode is in the Prius classic. The newer Priuses have electric A/C and may not do this.

Anyway, I think that the answer is that slight motion and slight shuddering when the engine starts and stops is normal. You generally won't notice it much when you are moving.

(Long time Prius-owner, but new to this list)