R56 Auto Trans - Gear Symbol Showing on Dash, In limp home mode (no gear shifting)

[Hoffman]

Trying to fix Auto Trans error showing with gear symbol on speedometer display. The Mini says in one low gear as a limp home mode.
Code from manipulating display with turn signal button shows CC-ID 420 (Electronic Transmission Control (EGS).
* Problem occurs after driving and sitting for a few hours then starting again.
* Sometimes problem goes away, but re-appears after running and sitting for a while.
* I checked the transmission level with the warmup, removing the plug, then adding a little fluid to let it drain and confirm proper level according to the level tube in the pan. On a side note, why was checking trans fluid level made so difficult - probably because of the BS Mini claim that its supposed never need checking and fluid is good forever.
* I Replaced valve body about a year ago due to hard shifting and Mini worked great after valve body replacement until recent problem described above.
* Changed out transmission electronic controller with a used one. No difference.
* Checked the cable connections going to transmissions for fluid leak by that I read is an issue where the fluid may short out connectors. Connections are dry and intact. I cleaned them anyways. No change.

I read where it may be a faulty transmission temperature sensor mounted in the valve body. Has anyone come across this issue. I am not finding guidance on how to replace the temperature sensor on the valve body. I hope I don't have to remove the valve body.
Thanks.