That tells a lot

What the diagnosis said was that the selector sensor is faulty. It's part of transmission gear changing sensor - when you press your fuel pedal, the transmission fluid presure increases, which sends signal to change higher-ratio gears. It appears the sensor didn't sense the signal.

It should be changed, however, do not go to dealers to do so. The change is very simple, the module shouldn't be that much. You can bring this diagnosis report (wipe out the price) or type the report in a separate paper without price to reputable MB shops to get an estimates and find the one you feel comfortable with to get it replaced. Good luck!