Hi. Have you tried manually selecting for the vehicle? I would not relying on the auto recognition of certain vehicles, as it works for some vehicles and some times it does not work. Also when using the 38-pin adapter if vehicle supports it, this will give more advanced diagnostics capabilities. The OBD-II 16-pin usually give the generic capabilities of typical generic scan tools; Still worthy though when only checking for emissions related info for it faster and simpler at times.

So, try giving a shot by manually entering/selecting vehicle or Benz in this case.