So I was checking out the Mercedes forum on the 722.6 transmision and this is what I learned.

FYI:
When the ETC detects intermittent or active problems, it prohibits gear shifting, in order to avoid serious transmission damage. "LIMP HOME MODE"

"There are two different types of Limp Home modes, depending how serious the problems are. The names of these two different Limp Home modes may sound counter-intuitive but that is what Mercedes used.

Mechanical-hydraulic emergency running mode (This is the light duty Limp Home)

In this Limp Home mode, the transmission locks onto the 3rd gear or the last known “good” gear.

This particular Limp Home mode can be reset by turning the ignition off and then on.

This mode could set generic OBD II code and also intermittent code in the ETC.

Electric emergency running mode (This is the bad boy )

In this Limp Home mode, the gear engaged at that time is retained and the assigned fault code is stored. After a shutdown, wait for more than 10 seconds, and restart, the transmission is locked in the 2nd gear and reverse gear only. When the shifter is moved from “P” to “R” or “N” to “D”, there is a huge clunk.

The transmission will be in this mode until the codes are cleared from the ETC by Mercedes HHT (Hand Held Tester) or SDS (Star Diagnostic System) or some third party special scanners or even the reversely engineered ones. Generic OBD II scanners cannot clear these codes from the ETC (although they can clear the corresponding generic OBD II codes).

When the transmission is in this “electric” Limp Home mode, it feels like it is completely shot. Many times (actually I will go out the limb and say most of the time) you do not need a rebuilt transmission or a new ETC."