Check Valve. Crankcase Ventilation.
PCV Valve.

CHECK VALVE

Fits C30, C70, S40, S60, S60 Cross Country, S60 Inscription, V50, V60, V60 Cross Country, XC60

5CYL. B5254T12. 5CYL.
PCV Valve
If your PCV system is malfunctioning, you may notice any of several symptoms: if your tailpipe smokes or your engine idle speed is high or erratic, the PCV valve or its associated parts may need service. You may also notice that the dipstick in your 2016 Volvo XC60 won't stay in the dipstick tube, or that your oil cap hisses as the engine is running.