grober
MB Master
There are possibly 4+? discrete components involved in the 722.6 transmission control signaling the gearchange module [ PRND+/-] , the TCU, that round connection plug and the so called conductor plate inside the gearbox- might be a fault in any of them. The transmission sub- system talks to the engine to give and receive information- if its faulty it will tell the engine management system to go into limp home mode to protect the transmission. That's why you need more precise information. The modern Mercedes Star system is quite expensive so you are unlikely to find it outside a dealer or mercedes specialist workshop and of course is only as good as the technician using it. Its usually a word of mouth recommendation thing.