I recently bought our first MH (a used Winnebago Via) with the same Mercedes 188hp turbo diesel and had similar problem. Also discovered that the first message I got "Check DEF fluid. See Operator manual" needs to be rest by dealer! Ours would not go out even though manual says it would. We had it at Mercedes/Sprinter dealer and after they replaced first part I made them take on a road test and sure enough it came back. They finally replaced both "NOS" (?) sensors and problem gone for now. Was getting some type of message, either this or the 16 restarts left - every 100-120 miles. Drove 200 miles with no message - small victory!
