You cannot get the car out of limp mode without a Mercedes HHT or a Snap-on scanner with the right module.

I learned this the hard way with a 1997 SL320 that had a bad speed sensor on the conductor plate. Even after you repair the fault, the system will still remain in limp mode. You'll have to find a friend that has a Mercedes shop or go to the dealer and ask them to reset the TCM.

Your TCM is probably fine. It just needs a reset.