No AWD - rear wheels not engaged. Duty solenoid C? TCU?

[UberRoo]

I'm just hoping someone has had a similar experience and can advise me. My transmission has been functioning flawlessly for the last 116k miles, but has suddenly lost it's ability to use the rear wheels. I have a latent trouble code 25, "Engine torque control signal" but have had no current trouble codes whatsoever.

As I understand it, when duty solenoid C fails, you're basically stuck in '4WD' as it may be. In my case, the opposite seems to be true. I don't have a wiring diagram that details the transmission, but I do have a pinout of the transmission wiring harness connector. I don't entirely trust the pinout, but I did a basic continuity test of duty solenoid C based off the information I have and it seems to have low resistance, which indicates that it works. Additionally, both electrical failure and seizure of the valve should trigger trouble code 24. The valve seems good - why isn't it being triggered?

Has anyone else had their AWD stop working? Where can I find a complete wiring diagram of the transmission? Frankly, the solenoid is relatively easy to replace and not outrageously expensive, but I don't believe it's at fault in this case. I simply want to know how to test it with certainty without removing it - that, and to find the real problem at hand.

See the attached diagram. Any ideas?