Transaxle replacement: how to/DIY writeup?

I have a 2005 Prius with right under 95k miles. Recently on the last 2 hour leg of a 9 hour road trip the CEL (red triangle) came on, along with the yellow brake and VSC lights; cruise control stopped working as well. I could stop and cycle the car on/off a few times to clear all the lights and the car would drive fine for another 20 minutes, then the lights would come back. After a couple times I kept driving with the lights on to see how far it could go, eventually the ICE shut off and I was basically in EV mode. I stopped, reset the lights and kept driving some more. This time after the lights came back and the ICE shut off, a temperature icon came on the MID.
I decided to stop for a little bit and let the car cool off, then I went on my way again and decided to keep the car at 55mph (instead of the 75mph I was doing). It was 40F outside so I figured if I keep the speed low enough the ambient air should keep it cool enough. It worked and was able to get home without any more errors.
It's been about 3 weeks now and I've been driving around town without any issues, except for a howling sound that developed when accelerating and slowing down. I went on the interstate to try and re-create the error. Sure enough, after 20 minutes of driving ~70mph the lights came on.

I did a bunch of searching on this forum and google and was hoping it was the inverter coolant pump, but there was always turbulence in the reservoir. So I went to O'Reilly auto parts and used their OBD2 reader. The two main errors were P0A2B and P0A37 (Drive motor "A" temp sensor range/performance, and generator temp sensor range/performance). The other errors were left and right front wheel speed sensors (C0200/C0205), Accumulator low pressure malfunction (C1256), malfunction in HV system (C1310), open circuit in main relay 1 (C1311), open circuit in main relay 2 (C1313), capacitor malfunction (C1377), and U0293 (no communication or something to that effect).

I'm assuming all the other errors are just byproducts and that I just need a new transaxle, found a good price on a used one and want to tackle the job myself. I'm no mechanic but I've always worked on my own cars and can follow a write-up. But I've never worked on a hybrid.

Is there things that I should know before trying to do this myself? What other things should be replaced while there (gaskets etc)? And most importantly, is there a DIY writeup somewhere for replacing the transaxle?

 

Awesome, thank you.

 

Alright I got the old transaxle out and I'm in the process of transferring connectors/hoses/etc to the replacement.
Is there any seals I should replace before I put this other one in?
Should I flush it out (how?) to remove any debris that might have gotten in there while sitting at the salvage yard. If so, would it be fine to use cheap transmission fluid to flush it with and fill it with the recommended toyota fluid when done?
Does the torque converter have to line up a specific way on the spline?

Did I mention I've never replaced a transmission before?

 

I'd say it took me about 7-8 hours, split in two days, to get the transaxle out. I've never done any sort of work involving a transmission before so I learned a lot these past couple days. I worked slow, made a few trips to the store, installed an engine hoist, took some snack breaks, etc.

Your writeup was great and definitely helped a lot. I did make note of a couple things that could be added/changed but nothing major. I'll message you when I get everything back together, which I think will be the hardest part.

 

Oh also, the replacement transaxle had all the wires cut so I have to open it up to transfer the big orange wires. What kind of sealant should I use to seal it back up (the factory stuff is pink looking).

 

Thank you for all the info, I really appreciate it.

One last thing (I hope), the "new" transaxle doesn't have the aligning dowel in it like my old one does. I tried removing it to use it but I doubt it'll be useable by the time I get it out. I'm guessing it won't hurt anything if I don't use it, besides making it a little harder to bolt up, right? (I still have one on the engine side)

 

No they're a couple hours away.
I'll go ahead and order one online along with a couple other things. I've had nothing but bad experiences at the dealer here so I'd rather not give them any money. I'm not in a rush so I'll just wait a few days for the stuff to get here.

Would you happen to have a part # for the tranny sealant?

 

Found the part # for the sealant: 00295-01281

Also found out these cars don't have transmission fluid filters, one less thing I need to order.

 

Alright, got most of it back together. Couple questions.

a) Where is the ground strap that connects to the inverter? I don't remember re-attaching it (or taking it off in the first place) and don't see it anywhere.

b) Where is the bleeder screw for the coolant? Is it the one that is attached to the inverter? The're a sticker under the hood that says it's on the side of the radiator but I don't see that.

c) How do I refill the transmission fluid?

 

I got it all back together, figured I'd try to start it before I lowered it back down, and it won't start.

If I press the power button with my foot on the brake the car turns on like it normally would but instantly shows the Big triangle light and a problem warning on the MID. It also does not let me turn the car off with the foot on the brake.

Without the foot on the brake I press the button twice, and same thing except I can turn the car off with the foot off the brake.

I pretty sure I plugged everything back but I may have missed a plug on the inverter. After I unplugged them all I decided I should count them to know how many to plug back in and I counted 13. When I plugged them back in I counted 11 because one of the 13 was for the wipers and I may have counted the plug on the driver's side of the inverter with the yellow sticker on it (though I didn't actually unplug it I just unbolted it).

The tranny I think only had 4 plugs and I got all of those.

I don't think O'reilly Auto Parts usually loans out their scan tool but maybe I can get them to let me take it home for a few minutes.

Any ideas on what to check or how to figure out what's wrong w/o an OBD2 scan tool?

 

Ahhh, I hope that's it, I didn't do step 3. Though I can see the charge level of the HV battery on the MID.

 

Well that was it. Took it on the interstate for ~40 mins at 75mph and no error. It previously only took about 20 mins for the error to pop up at those speeds.

Now I need some new wheels/tires because these ride horribly.

Thanks for all your help Paul, I couldn't have done it without you. I'll post up a few notes later tonight.