Blown Transmission - No Warranty

Good job and good write-up. Any chance you have any of the old Wth-AS fluid left that you could send out for a Used Oil Analysis? This may be able to tell you if the trans fluid may have been an issue.

 

Nice pics, thanks for the info.

One thing though, I'm a little confused about the mileage. You commute 80 miles a day and yet in 4 years you've only gone from 53k to 67k miles? Or did this "until one day, at 67k miles" thing happen about three years ago?

 

great job, thank you for posting. i think i have read about a small number of these problems in the past. glad you were able to diy and save a ton of money. welcome to p/c and all the best with your new tranny!

 

I have to say, coming from an EE that's not that mechanically inclined, that's quite the DIY project, well done! Great pictures of the damage of the motors. If I had to guess, the continued driving past the initial problem is what I'm assuming fried MG1 that bad, but that still doesn't explain the first failure to begin with. MG1 would've had to reach fairly high temperatures to have the coils burn out like that! (see below)

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On a very related note.. I had a co-op job once where I did some testing of a vacuum handling robot, which failed either because of disabled servos, or because the motors remained energized after failure. I did a worst-case scenario test on the overheating robot to see what temperature the windings sustained to see if there were any safety issues -- i.e. potential of a fire.

I'm not sure what the maximum winding temperature of MG1 is, but for the test I was doing I went about 10 deg C higher (unfortunately lost power shortly after 5 hours into the test) than the maximum winding temperature spec of one of the motor's windings without causing a fire. (MFR max temp of windings was stated to be 155 deg C)

Realistically under normal operation, the robot motor winding temperatures should not have exceeded 40 deg C; the current drawn from the wall socket before the failure was nominally ~2A DC... when the robot failed the current draw went up to 17A DC!

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Kinda curious what others more familiar with transmission failures on Gen IIs have to say on the matter! Also, OP, props on getting money back on the old metal of the bad transmission, and great first post, haha. =)

 

Could this all have been saved if you'd have acted immediately on the warning lights, taken the car in and perhaps found the inverter was bad; or would that not have made the slightest difference?

 

A truly outstanding first post, and congratulations on your successful repair at such a low out-of-pocket cost. Thanks very much for the teardown and fault analysis.

DTC P0A7A is the important code logged by your car. I don't suppose that your service invoice lists the three digit info-code associated with that DTC, which provides a finer level of detail?

Regarding the two photos that I copied from your OP, are those two burn spots in close proximity to each other? Might they have been caused by the same wiring insulation fault?

I believe that the smaller MG is MG1 since it has a lower power capacity than MG2. MG2 always spins along with the transaxle output shaft. MG1 has the job of spinning forwards and backwards at whatever rate is needed to allow the gasoline engine and MG2 to spin at the rates required by the hybrid vehicle ECU, given accelerator pedal position and vehicle speed.

You had asked what was the cause of the problem. My guess: it happened when you floored the accelerator because there was a surge of current into MG1 which has to quickly adapt to the gasoline engine's RPM speeding up. That current surge found weak spots in the stator wire insulation and caused a high voltage arc from one winding phase to another, resulting in burn marks. There is up to ~500V three-phase AC voltage produced by the inverter.

 

Great post... So great I'm tweeting a link to it first thing in the morning! It's exactly the kinda of post that will fascinate someone thinking about buying a Prius... It's hard for people to understand how a hybrid engine works and even thought there are some great videos that explain how the moving parts work via animation and models, this is the first post that really shows how big and how heavy all these parts are... I especially like getting the weight of each type of metal thanks to you selling it at the junkyard. Brilliant work RedboneCoondhound! A very valuable contribution!

 

In the manual, it is stated that normal street driving should not reach higher than 80C. I see 70C often going up hill on a hot day, with A/C on. The windings can go much higher before a DTC is stored, but 70C is already burn your finger hot.

 

Well done on the cost! Yeah, 2nd Prius PSD failures seem rare, at least on ones w/that low a mileage.

Boy, I'd sure hate to have mine fail during the time I own the car. I'm more than 1.5 years past the powertrain warranty. I don't have the skills nor equipment to do a swap if I needed to.

 

so there is some benefit to my driving like grandma?

 

I'm driving a 2005 with almost 100,000 miles and I don't baby the transmission. I'm all for replacing the fluid and I don't drive it like a drag racer but I wouldn't baby the prius just because you saw one fail.

 

Undoubtedly caused by incompatible 3rd party ATF attacking the insulation ;_>

 

Shocked that Toyota doesn't cover mg replacement as part of 100k hybrid warranty....if transmission fluid change done by toyota or proof of purchase for toyota ws atf. I certainly thought mgs part of hybrid warranty.

 

I agree that the mg's should be part of the Hybrid Warranty and not the Powertrain Warranty since they are such a vital part of the HSD. The Warranty and Maintenance Guide Manual spells it out though, the Transaxle/Motor/Generator is spelled out under the 60 mos / 60,000 mile Powertrain Warranty.

 

As a new 2007 Prius owner and somebody who is very mechanically inclined with years of experience, I find this very reassuring that replacing major components of the Prius are (somewhat) user friendly.

Looks to be a straightforward transmission swap very similar to any modern FWD vehicle. Not too shabby at all. To make matters better, I checked car-part.com and locally used low mileage Prius trans's are going for pretty cheap, relatively speaking ($350-$800). Hopefully Ill never have to go "there" but I will definitely be changing 4 quarts of Toyota's world trans fluid out of that thing every 30,000 miles as preventative measures!