Help diagnose possible bad transaxle damper

This is in a 2012 plug in prius, 194k miles on it. I've owned it since 86k, and done a lot of preventative maintenance. EGR was done ~40k miles ago, and was not clogged at all. OEM water pump 80k ago. Does not burn a drop of oil, or coolant. transaxle fluid has been done twice, engine and inverter coolant twice. Plugs were done 94k mi ago.

Today, while my wife was driving, it made a loud noise, then kept making noise while driving, and seemed to lose power, but she was able to pull off and call me.

When charged, and running as an EV, it's normal. no noises, no issues. So seems like it must be "upstream" of MG2. It is rougher than usual transitioning out of EV/ECO when the engine turns on. I will say, since i've owned it it has always had a bit of a judder coming off EV/ECO when the engine turns on, just a slight hesitation feeling. But it is now worse. If i baby the throttle so the engine comes on more gently, it is not as bad.

I have not pulled codes yet, but there is no CEL on.

I'm guessing one, or more, of the damper springs are broken. Any way to confirm this? or what other diagnostics would folks recommend?

For the price of new plugs i'm thinking i'll just change them and be sure this isn't a misfire... Other ideas?

 

Ok great, thank you @ChapmanF I will check this inspection window and report back. Fingers crossed for no spring chunks…

I can’t speak for previous owner, but afaik I’ve taken good care of this engine. Possibly this is a plug in Prius thing, due to the fact the engine will kick on at high power draw in EV mode?

 

ok. i pulled codes, the only one confirmed is U0146 - "lost communication with Body ECU". i'm using an older OBD2 scanner, so likely will buy a newer one to make sure this isn't a me thing.

I removed a cover on the back of the flywheel, seems to be called the "starter hole insulator" per Page 11 of this book.
There was also a little plastic cover on the back of the flywheel housing, at the bottom. I could not feel much through these... and don't have a boroscope to really check for pieces. however, when i moved the flywheel back and forth, it made a very loose sounding metallic noise.

Is there another cover? i don't have a lift, so really couldn't see one, nor in any of the images in the link above.

i'm going to swap plugs preventatively... about due anyway, but this is seeming unlikely.

Any other suggestions to diagnose this myself?

Also wondering if there are any ways to avoid shocks from MG1 if this is the issue... I can, for instance, not charge the battery so it runs EV less. or would running in B mode help? Hoping to avoid a sheared transaxle shaft...

 

With a "pro" scan tool i've confirmed: U0146, B1206, B2321. I don't know if these codes were present before or after "the event", but no CEL has been on for at least 1+ years.

I swapped plugs. None were wet, and overall in OK shape. Center electrodes seemed fine, but ground electrodes all had some uneven wear, and a max gap of around .055. The old plugs were NGK OEM, but not double platinum, wear seems about normal for ~95k miles of use. No noticeable difference after installing the plugs.

Still hoping for some input on any of the following:

• Is there another way to confirm/check/diagnose if this is a degrading transmission damper? I can probably borrow a boroscope if this is the best way.
• This is my daily, so wondering the best way to avoid shocks from the engine/MG1. Thoughts?
  • Mainly i'm planning to "save" any EV range i have as a "just in case", so i could limp it if needed.

 

Yes, as stated in the #1 post, done 40k miles ago. not squeaky clean, but none of the EGR passages were clogged. fully cleaned at that time. No coolant consumption, oil stays extremely clean, no oil consumption at all.

Thanks for the Gen2 post, i hadn't looked over there. The Gen3 transaxle has a second planetary gearset, but don't believe this changes the symptoms. no uneven operation experienced, but if i really hammer the gas, i am now hearing a "clunk"... unfortunately this seems to be confirming my suspicions.

I am going to try and borrow a boroscope this weekend and get a view inside the "bell housing" for the flywheel and damper and see the real story.

As a reminder, this is a Plug in Prius. I thought i recalled that with the Lithium Ion battery there is a higher current available to MG2? I know the regular Gen3 will not get to 62MPG on battery / MG2 alone... so wondering if this is related to a difference with the Plug in Prius. That aside, with 194k miles this is no spring chicken