P0171,P0174 NISSAN Pathfinder 2001-No running problems. Extensive dealer eval-no cause found

Question

2001 Nissan Pathfinder 62,000 mi. P0171 and P0174 began occuring after gas fill, MIL would sometimes turn off after several drive cycles, but now recurs usually after one drive cycle following reset.  Independent dealer eval (dealer level-- good shop) showed normal fuel trims, normal emissions, no discernable leaks. Nothing abnormal found.  Starts, runs flawlessly.  Fuel mileage unchanged.  Sort of reluctant to let the local Nissan dealer repeat eval.  A faulty cam angle sensor cost me over $500 there.  Front O2 sensor, air mass sensor?  Wondering how to proceed so I don't get ripped for what is likely a simple problem.  Air filter OK, replaced fuel cap.

Answer 1

Check for leaking intake system, If no leaks found you should try getting the Engine Control Module (ECM) reprogram first. If the problem persist you may have to replaced both front O2 sensors. Without out testing the vehicle it's difficult to diagnose if the problem is the O2 sensor or the Mass Air Flow (MAF) sensor. Due to the age of the vehicle you should start with the O2 sensors.