4x4 problems gm dtc c0321-06

Working on a 2007 chevy tahoe with 5.3 dtc c3021-06. Whats the best way to diagnose this owner tried new tccm and encoder motor at one time. So now it seems encoder is old and tccm is new. Still has code. No 4x4 also I scanned and switch is responding. This has a np8 rpo code for transfer which is odd because it has a circle switch for selecting 4x4 options. Anyway this 07 has 05 brakes and was built in 12/05 but, has the newer body. Just looking for best way to go about this or most common issues...

The transfer case lock solenoid is released by being energized. This is accomplished by grounding the lock solenoid control circuit during gears shifts, and in the AUTO 4WD mode.

Does this wire change state when going into and out of these modes? Do you have ground there during gear shifts?

Can you post code setting criteria? It says lock solenoid circuit short to ground? Is the wire shorted to ground between solenoid and tccm?

It's in attachments. Short is certainly a possible cause. plus "This DTC detects an open lock solenoid coil, open motor lock control circuit, or an open motor lock feed circuit."

I'll try that on monday right now owner has car for hunting

That's what I need to test and help with.