Had bad solenoid. First tried to replace the 2 common failure solenoids, no change.
Swapped in electronic part from other tranny (potentially damaged when oil pan was knocked into mechatronic control board). got another solenoid code.
Decided to buy complete matching mechatronic unit.

Swapped in.

Code (00020) verified.

Tried to run basic settings group 061: error
Ditto 060.
ran 062, 067, 068, 065, 063, 069.

Test drive: no R, not shifting.

Initially, codes like

18261 - Powertrain Data Bus
P1853 - 000 - Implausible Message from ABS Controller

17161 - Pressure Control Solenoid 2
P0777 - 000 - Stuck ON

Last check, did not get codes.

What else to test, check, troubleshoot?