MG2 rumble / vibration

This may be the reason, however, we need more data from other members. So far we only have 4 reports that gen 3 does it, and only one report from gen 2 owner who does not have this rumble. Hopefully will hear from other gen 2 owners to confirm this... I also wonder why they changed the design on gen 3 and did away with the chain?

 

Are there any reports of chain failure in gen I and II? I did a quick search and did not see any reports on this forum. But it seems that the chain will absorb the resonance frequency from MG2 cogging and thus will not transfer it to the body of the vehicle. That is why Gen II owners do not feel this rumble.

I saw there is a TSB out there for engine mount replacement. I wonder if the new engine mount will reduce this rumble feel; however, my prius is built 8/11, so I am not sure if it is covered by that TSB or not. There is a way to tell based on your VIN number, but I could not figure out how yet...

 

This is the first time someone reports this issue on Gen II, very interesting. Perhaps we should ask this question in Gen II section and see how many reports we get. I called Toyota USA today and had them log this issue into the system. They said that the service manager from the dealer will be in touch with me soon regardin this issue. We apparently still have only 4 clear reports from Gen III owners on this forum. Unless more people report on this issue, can I assume that the issue is random and not consistent?
To test:

Have car in ready with ICE off, in D position, foot on the brake
Release the brake but do not press the accelerator
The car will creep forward very slowly
Watch for very low frequency short rumble in the cabin and a very slight momentary vibration on the steering wheel at a speed of about 1 MPH.
Report on here if your car does it or not

Thanks!

 

Yes, this is a different issue, unrelated to this rumble.

 

Update - got a call from the service manager today asking to come in and check the rumble issue. Was able to stop by after work, the manager was still there. He seemed to be very interested about the issue, but stated that I am the first person complaining about it. They also had 2 of their mechanics with a laptop in the car with us. All three of them confirmed this rumble issue, and all three stated that I am the first one who noticed it. The mechanics had no idea what is causing it. We test drove 5 other Prii on the lot, 4 of them did it, the 5th one either did not do it, or it was so faint that we could not feel it.
After about 2 hrs the manager stated that they will have a toyota engineer come down within next 3-4 weeks to look at this issue and they will call me to come back. Right now they could not offer any solutions. I was surprised that nobody else complained about it, but than I thought that for an average person this issue is very hard to notice. Perhaps this is why only 4 people on this board confirmed it.

 

Update,
The toyota engineer came out this past Friday and I met him at the dealership. Very nice guy, he was an actual field engineer, not one of those "regional reps" who normally come out to look at complex warranty issues. He took his time to go for a test-drive with me, confirmed the rumble and immediately stated that this is due to electric motor cogging. He even showed me some toyota technical documentation printout where this phenomenon was actually described. The bottom line that this is considered "normal" by Toyota, I was told it is part of the design. When I asked him why they did not engineer this out like they did in Chevy Volt, he said due to cost.

 

Update for those who followed this thread from start: I just received a letter from Toyota USA stating that their engineering team thoroughly investigated the issue and that the stated phenomenon is a design characteristic of this electric motor. They then went through rather long explanation of what "cogging" is, and stated that this is not a defect and all 2010 -2012 Prius models exhibit it. The letter was signed by an engineer. I am impressed that somebody took their time to write me a two-page letter with detailed explanation. Perhaps Toyota engineers are frequent on this forum?