The Nissan Path

Greetings all
I have been searching this code P0001 codeon the
this forum and general internet search etc.
I see on my scanner is FVR open circuit/ solenoid. I also checked the Haynes manual and P0001 is not there. I have tried to reset the code and it comes back within 15 minutes of driving. I have already replaced bank 1 cat.
Then it said to replace bank 1 O2.
Now it says FVR circuit. Can someone please assist me with some suggestions on how to start to diagnose this?
All the best

I've never ran across that code on any Nissan before. What year and engine is your Pathfinder? What did you use to retrieve this code?

I am now getting a MAF code
I bought a MAF from advanced auto. It is a spectra
I had the battery disconnected for a few hrs since I was doing some other maintenance. The truck idles horribly now. I cleaned my k&n filter before installation of the MAF. Now with either MAF the truck does not idle well. Any suggestions will be appreciated. My wife drives this thing and I don't want any nasty surprises with this Truck.
Many thanks

Any time you disconnect the battery for a long time or make changes to the air intake and/or replace a mass air flow sensor, you often need to do an idle air volume relearn.

Can someone please paste a link to this procedure?
The truck went to the dealer. 400 bucks parts/labor for new MAF.
Thanks

update
now the dealer said it needs a wiring harness $2000 lol
the truck feels like hitting a wall when you press the gas. seems like ignition/fuel