I meant to reply to this earlier, as this happened to me fairly recently. My 2016 GLC 300 4Matic had a failed pcv valve a little over 30k, my dealer said this is a fairly common failure point on these cars. Unfortunately, the Mercedes engineers have made this job exponentially more difficult of a job due to the location of the component. What is more frustrating however is even though they know this is a component that is a likely fail point, they still put it in a pain in the a** location. Not a terrible replacement to do yourself once your warranty is up if you keep the car, just time consuming due to the placement of the component. Dealer covered it no questions asked. These “breather valves” for the crank case essentially modulate as necessary to provide adequate crankcase ventilation. This modulated voltage signal comes from the car’s computer and varies based on engine conditions. The issue your experiencing could be a bad signal to the valve (in this case it’s a modulating solenoid) itself, where in my case the oil over time had gunked everything up and caused the valve to fail open. When the ECU sees a different output as compared to the input signal to the solenoid, it threw my CEL. Like I stated earlier, yours seems like a signal issue rather than a component issue as mine was, but they will probably replace everything anyway. Good luck and let us know how everything goes. I also could be totally wrong, this is just my understanding of how the system works on the car. But like I said keep us posted. Also not that big of a deal if handled promptly but over time could cause a more serious issue with oil in your intake system.