I have a 2011 s40 t5 and a few days ago it started whistling. Did a google search and found that it's a common PCV diaphragm failure. It ran for a few days then the check engine light came in. Still ran but today I was able to replace the old box with a new Volvo brand pcv box; 2 hours later it was replaced.

Problem was immediately after installing when I went to test drive it, the dash said Power reduced (forget the exact phrase) I couldn't get past 2k rpm. Pulled it back home and scanned the codes.

Checked all connections, hoses, etc and couldn't find anything out of the ordinary. Install was easy.

Checked codes and had a P0128 and P0171. Any reason why The PCV being replaced would cause this?

 

Did you forget the fuel pressure sensor connector? Or maybe a pinch a wiring harness?