Fuel pressure questions

My mechanic scanned my 2012 Prius because the check engine light came on no other symptoms we’re obvious the car seems to run well. The initial problem code title that came up was inefficient catalytic converter. My mechanic also did a live scan with the car running and noticed the fuel pressure was incorrect supposed to be around 45 pounds but he read that it was only around 15 pounds. We are in the middle of trying to figure this out, the questions now are how is the fuel pressure regulated? Where is the fuel pressure regulator? could there be a fuel filter issue? It’s gotten pretty cold now and the check engine light has gone off, but he thinks my problem is in the fuel system with the pump or the regulator or something so any input to help me diagnose and fix this problem would be greatly appreciated. Thank you oh by the way the temperature yesterday was 8° I’m in the middle of Wisconsin and I did add some isopropyl heat alcohol may have had something to do with the check engine light going off but I don’t know that.

 

Thank you