The problem may not be with the kick down switch. Both the figures you give in your post are very close and it seems to me that if the kick down wasn't working or putting out a proper signal the car would not know you have pushed the peddle down and thus would continue in the current gear without going into limp. Do you have any problems when using the transmission manually or just in drive?
My suggestion would be to get a deeper scan with Mercedes software to access the transmission and engine codes at a deeper level than an ordinary OBDII scanner can do. The generic codes do not give enough info to solve your problem.