I found this on Volvoforums UK:

I replaced my pcv over the weekend and was just about to take out the solenoid and replace it when I noticed that one of the wires leading to the solenoid was totally ripped apart! So an error code of "circuit open" can sometimes mean just that - a busted wire!

I share this because the root cause was that a while back, some of the black corrogated plastic tubing that protects the sparkplug coils, etc broke apart on me so I took some of it out without really thinking that I needed to replace it. Well, if you don't replace it, it becomes very, very easy for these wires to get stuck over one of the mounting bolt holes for the plastic engine cover. When this happens, you can very easily crush the wire when you put the cover back on which is what I did. Not sure how the dealership missed that seeing that you have to take the cover off to view the solenoid...anyhow, solenoid is fine, red wire is re-connected. All good.
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Keeping it running is better than buying new