I decided to start a new thread since everyone agrees my Yukon is very sick.
The dealership and my repair guys agree with the diagnosis of inverter and transmission.
Some of what I'm writing is based on information from the internet, Youtube, and other sources.
If I'm wrong please correct me so I can adjust my analysis.
My IT and electronics experience, along with a small amount of optimism, not sure where that came from, is thinking that you can't accurately diagnose a transmission problem without having first solved the power problem.
If the inverter has failed, ie: not consuming DC current from the HV battery and producing three phase AC current, then you can't say the drive motors have also failed.
If a horse is standing on your foot causing pain, you can't determine if your foot is damaged until you remove the horse.
I'm thinking if I replace the inverter / drivetrain control module, then we can determine the extent, if any, of damage to the drive motors.
GM says the drive motors aren't replaceable and only available as part of the whole transmission assembly.
I watched a YouTube video of them disassembling this transmission, not what I had envisioned about electric motors driving it.
GM wants $3k+ for a new inverter, I'm hoping I can find a used one for less, regardless after replacing the inverter I'm still a long way from the $16k GMC wanted for replacing both items.

I'm not sure what I'm asking for, kind of typing and rambling at the same time.
Do you guys/gals have any thoughts or insights into my idea?

This Yukon was our first adventure into the world of hybrids.
At this time the used car market is insane and people are paying incredible premiums for new SUVs.
I can't justify dropping $16k in repairs on a truck with a used value of $6-10k.
I really can't justify spending $60k+ on a new Yukon or similar.

Okay I'm done rambling.
Please discuss amongst yourselves and let me know if I'm crazy or just a little bit off.
I'm in central Florida where it's now summer so I'm not crazy from the heat but not far from it either.
Thank you for your time.

 

Your thinking is reasonable. I would add that you would want to check the transmission anyway to rule out a bad transmission damaging the inverter module. What makes GMC think the inverter is bad? Could it just be detecting a failed motor or phase cable shorts? maybe do some checks on the motor phases to make sure the resistance measurements match between phases. check between each phase and the shields. a short in the motors could possibly damage the inverter, but I would hope GM programmed a fail-safe into the inverter that would detect over-current and open the circuit to protect itself.

One failure that has been seen before is damaged motor phase cables between the transmission and the pinch welds nearby. the phase cables shield gets damaged. Your codes sound like the actual phase voltage is shorting out rather than the shield, so maybe the damage is more extensive? Check the 6 orange cables going from the inverter to the transmission.
Take a look at this thread about the pinch weld and the motor cables.

Looking into your codes a bit more, it appears the problem may be in the HV cables between the hybrid battery and the PIM (power inverter control module):
Codes P1AF0 (Drive Motor 1 Control Module Hybrid Battery Voltage System Isolation Lost) and P1AF2 (Drive Motor 2 Control Module Hybrid Battery Voltage System Isolation Lost): The drive motor generator power inverter control module(PIM) contains two motor control modules(MCMs). Each MCM measures hybrid battery high voltage(HV) with several internal sensors. The MCMs test for loss of isolation(LOI) between either the HV positive circuit or HV negative circuit and vehicle chassis.
Did the GMC dealer or your local tech actually check out the HV battery cables? They could be shorting to chassis.

 

I doubt GMC or my guys examined the cables for damage.
This whole failure started when my guys went to start it after an oil change and replacing an ABS sensor on a rear wheel.
They said it made a loud whine like a jet then a slowing spin down sound.
My guess is the inverter sent voltage to the drive motor #2 which caused the motor spin up and down noise.
I'm also guessing those two AC motors probably spin with some serious torque and rpms so any surge the inverter can create wouldn't be more than the motor could accept.

My repair shop doesn't have much experience with our hybrids but he's done considerable services on the Prius and other popular cars.
I've printed this thread and the other one you linked regarding inspection of the cables.
I'm going to let him read through this and get his opinion using this new information.
I would love to get our Yukon running again for only $4k (only, can't believe I said that) but if he's not convinced then I will give up and put it up for sale for parts.

Thanks for your help.

 

Any update? I’m receiving transmissions motor fault codes saying there’s a short.

 

do you have the fault code? I might be able to look up a trouble tree for you. it might show a way to test the motor before replacing it.

 

P1AF0 and P1AF2 currently no negative impact to drivability. Only seeing service hybrid system message

 

so I'm not sure where to start with this one. the trouble shooting is a bit in depth too. here's the 2 things I have for it looking up those codes up. any chance you can read the freeze frame data? my trouble shooting software which isn't gm and the hybrid diagnostic file doesn't seem to agree 100% to me. and I have no idea how your truck is running. usually any loss of isolation of the 300v DC and it shuts everything down instantly.

here's both.

 

I gave it to a friend to play with.
When he opened the transmission he found chunky fluid.
The fluid was good but he thinks the arm for the PARK mode may have been damaged and exploded inside.
He parted it out to some of his friends.
So ended my adventure into hybrid cars.
I had a bad first experience but won't necessarily give up.
My biggest concern is none of the current hybrids will drive without their big battery.
With the majority of the hybrid batteries being made by our enemies, I'm a little leery.

 

When my OEM battery was failing, I thought it was a transmission problem.

The real issue was .not enough power getting to the motors causing the engine to rev up in an attempt to create more power.

I don't know what symptoms your Yukon is showing as I haven't seen the other thread yet, however, when I went to a local trusted transmission shop he told me he has never yet once had one of the hybrid transmissions in for repair ever.

Apparently these transmissions are bulletproof mostly because 90% of the time you're using the electric motors.

Parts are available used. I ended up putting a new steering rack in mine from the auto recyclers.

Can you send me a DM with the link to the other Yukon posts as I've put about 200,000k on my Silverado hybrid since I bought it, I may have experienced something that may be helpful to you.