This guy obviously has great diagnostic skills. Something to aspire to. I did find it interesting where he chose to start his diagnostic journey though. I know it's easy to be an armchair mechanic, but after figuring out the transfer case was engaged in 4wd but the dash lights weren't verifying it was, I would have first suspected the switch on the transfer case was bad. It wouldn't go out of 4wd, because the switch was already reporting to the 4wd ECU that it was in 2wd. And, it wouldn't show it was actually in 4wd, because the switch was permanently reporting the 2wd mode.
He went down the rabbit hole of analyzing the wiring diagram for the ECU and testing all the circuits which probably ate up a significant amount of time. I guess what I'm trying to say is with any diagnostics, it's a benefit to know what would be the most likely culprit for the problem at hand and test that first.
I diagnosed a similar issue on a GX470 for anyone that's interested in watching it.
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