My 2006 Sedan has been giving a P0171 code for around a month now. I took it to my mechanic to see if he could find a vacuum leak/diagnose the problem, he said that there was no vacuum leaks and suggested to replace the MAF so I did. It seemed like that did the trick for a week then the code came back, I just got it back from a second mechanic who also could not find the specific reason but he suggested it was the O2 sensors and quoted me $700. I don't really want to pay for something that might not even fix my problem. Does anybody here have advice on what the problem could be?

 

That code is basically saying the ECM is having to compensate with too much fuel trim to correct an unspecified lean condition. This applies to BOTH engine banks.

First check the PCV valve, unscrew it and shake it to make sure it rattles, if it's not rattling and stuck open it will continuously suck crankcase air. Also check all 3 of the PCV hoses, they should be tight and unable to spin on the nipple without quite a bit of pressure. The one below the throttle body does not have a factory hose clamp for some of the later year models so you should add one.

Next pull and inspect the spark plugs for a single lean cylinder, this would indicate a clogged injector.

Lastly pull the fuel pump and replace the strainer filter/sock, if it gets clogged with debris you will start to deliver less fuel pressure to the rail which means less fuel to the cylinder / lean condition.

Alternately you can buy a fuel rail sandwich adapter like the one sold by Z1 Motorsports and use it to test fuel pressure since there is no factory fuel service port on the VQ engines.

The O2 sensors can be monitored to see if they're working, not sure why the mechanic would just assume it's the issue, you might consider going to a mechanic that actually troubleshoots the issue instead of throwing parts at a car. Nissan 1 hour diagnostic is about $125.

 

Swap the O2 sensors left to right and see if the code changes sides

 

what fixed the problem or what was the problem? I’m having trouble with this right now.
it’s not my pcv valve it’s not my spark plugs and my air intake is good.

 

Smoke test the intake and exhaust and look for leaks.