The 01 Pathy's CEL came on. It's giving me P0171, bank 1 running lean. A few I've talked to indicate that the MAF sensor is most likely the culprit.
I followed the FSM guidelines for diagnosing this trouble code and have found nothing out of the ordinary. The last thing to check is the MAF sensor/meter. I checked the air flow rate with my scanner it is is within the factory perameters outlined in the FSM. At idle, the FSM range is 2.0-6.0 gm/s. My Pathfinder is 2.46 gm/s. Gas mileage is not any different (17 city and 20-21 highway). Also, no noticeable engine power loss is felt.
I am going to replace the MAF sensor in the future, but I am trying to figure out how urgent I should be acting. I can't figure out why a trouble code is coming up when nothing seems to be malfunctioning. Any ideas? No one at the Pathy sites seem to have any more info. Maybe some of you Nissan Techs can offer some input. Thanks in advance.
Puzzled,
Aaron
2001 Nissan Pathfinder LE 4WD Loaded -113K miles
1991 Honda Accord DX coupe 5-speed- 101K miles

Most likely it is the mas/air flow meter. Even though it showed to be within range, it can still be bad. I have seen many cars and trucks come in with no check engine light on, and the air flow meter is the culprit.
If you replace the air flow meter make sure you put in a factory nissan air filter. They will not warrenty the part if it goes bad, if you don't put there air filter in during replacement.
You should also check fuel pressure, if it is low it will set that same code.
Dexter 260ZT Weee Weeeeeeeeeeee
Rebuilt 280zx engine, n/a efi, added t-3 turbo to n/a engine, n/a intake, turbo injectors, n/a afm, 83 5spd, 3.90 diff, new front end, new seat vinyl, carpet, console, 240z black diamond hatch vinyl.

Thanks, Dexter.
Your reference to "put in a factory nissan air filter" rings very true. When I bought it, the CEL wasn't on. Then after I did the initial maintenance, not too long ago, the CEL came on. I had used a generic air filter from Auto Zone. Then the parts guy from Nissan told me about the whole "only use OEM air filters on that Pathfinder", because of the MAF sensor issues. It just sucks that I will have to replace a $400 part for something as elementary as a generic air filter. Thanks for the response.
2001 Nissan Pathfinder LE 4WD Loaded -113K miles
1991 Honda Accord DX coupe 5-speed- 101K miles

it seems odd though because my parents also had a 2001 pathfinder LE with 4wd and we always used a fram air filter and oil filter. they just traded it in on a new '05 after putting 212k miles on the '01. the only time it went in to the service center was for an O2 sensor and to clean the sludge build up from the oil pan. the sludge blocked the oil pickup screen and dropped oil pressure to 3psi. after it was cleaned we had no other problems. it is a good idea to change the spark plugs if you haven't already. be sure to stick with the oem spark plugs and you should keep gas mileage at 20 or 21.
p.s. if an o2 sensor goes out change it asap or expect gas mileage to drop to 16 max for highway.
'79 280zx driver/project
'90 240sx sold :-(

Well, the parts guy said it was generic silicone filters. And the generic one I had was very flexible like a silicone/rubber type. As you know, the Nissan OEM filter is rigid. So there is probably truth to the difference.
I'm glad to hear the new Pathy should be as trouble free as my previous one. I had a 1990 Pathy V6 with over 250K miles on the original auto tranny and engine. Only thing I ever changed was an O2 sensor and maintenance items.
Great site! Thanks for the help and advice.
2001 Nissan Pathfinder LE 4WD Loaded -113K miles
1991 Honda Accord DX coupe 5-speed- 101K miles