My power steering failed while driving on the 2010 s550. Power steering Malfunction indicator came on on dash. What,s the cause?

The issue is likely related to a power steering leak at the power steering pump. Pretty common on nearly every Mercedes from this era. Reach behind the pump and feel if the back of the pump is wet. If it is, the reservoir and O-ring are likely the cause. The design is absolute garbage. there is no other way to say it. If you have no leak where the reservoir connects to the power steering rely on scanning the vehicle to identify stored power steering control module trouble codes. (should scan first anyways).