PVC/oil trap system fix

We have a 2005 Volvo XC 90. We have been told by the repair shop that we need to change the PVC / Oil Trap system and that it’s an expensive fix of about CAD 1700. Can anyone explain the mechanics of this system and why it should be that expensive? We have seen other information on the internet suggesting that this should be much cheaper to fix than the quoted CAD 1700. Thanks in advance for your input.

You got me courious. There is a YouTube video showing the procedure, lots of bits and pieces to remove and replace which means labor costs.
Just a quick look online the parts from Volvo run around $400 USD, saw some aftermarket parts for less, but quality, fit and finish MIGHT be lower than genuine OEM parts.
As to function, you can google “crankcase ventilation”. Or PCV function. Wikipedia has an extensive explanation.