The first 'limp' mode I experienced was a 1989 Grand Voyager with the (in)famous electronic-shift 4-speed autobox. When the trasmission computer determined it was getting no data, or 'bad' data it would cut power to the transmission shifter servos. The transmission would then hydraulically drop into 2nd gear and remain there. Quite an experience at 60 mph! Reverse and 2nd gear did not require any electrical power or computer to operate.

I expect that it's a combination of mechanically pre-set injector and spark timing and transmission shifting that will allow the car to run, and make forward progress. Just don't expect that M-B ride to which you're accustomed.

I hope this adds a little insight until someone else can give you the specifics on your car.

BCingU, Jim