your message is a bit sketchy, you mean it won't get out of second gear even when you shift it to neutral? or do you mean it won't shift to 3rd or 4th gear ? which is which? and then you say second and reverse work correctly???? most if not all MB will start on the 2nd gear (FYI) A limp home mode is when you cannot get any power and you literally limp home on a low speed even when you step all the way down to the floor of your accelerator pedal.

Hope you can be more precise with your data (problem) and I'm sure some one will be able to facilitate your question.