Urgent Question Regarding P0100 P0140...

[netwreck94]

Hey Guys,

I've been doing a ton of reading regarding my recent situation with these two codes. I replaced my Maf sensor with an OEM part about 10k miles ago and the car ran great up until yesterday. I've had an on an off P0140 (o2 sensor Bank 1 sensor 2) over the last month but it hasn't effected driveability at all save some lower gas mileage. However, yesterday on my way home I noticed the car running awful and put itself into safe mode with RPMS limited to 2300. I now have a P0100 code as well which is MAF circuit malfunction. However, I've read that if I uplug the MAF altogether the ECU will revert to default air/fuel mixture which should make the car run somewhat better...I noticed no difference whatsoever even after resetting the ECU. Could a this bad o2 sensor be causing the bad running and also tripping the p0100? Although that doesn't make sense either as I've had that code on and off for some time without any issue.

I also saw a short note about a TSB regarding the P0100 on the Maxima and all I could find was this...
"For example, a Nissan Technical Service Bulletin for the code P0100 In Nissan Maxima says that this code might be caused by "airflow sensor that has been damaged by air-ingested dust/dirt". " Could this be relating to the bad o2 sensor (airflow sensor?) P0140 that may be tripping the P0100? I'm just at a loss here. I find it hard to believe that my MAF could have failed again so soon, but also hard to believe that a bad rear o2 sensor could cause the truck to run so poorly.

Any help would be very much appreciated. As of now I'm having the o2 replaced on Friday and if that doesn't fix the problem I'll have to order another MAF...I'd buy the MAF now but don't want to be stuck with it should the o2 replacement fix the problem.

THank You

Evan

[Towncivilian]

Are there any air intake leaks? You say you replaced it with an OEM part - was this the $442 Pathfinder MAF, or the $89 Maxima MAF?

P0140 is inconsequential to the operation of your engine. It's a rear O2 sensor - its only purpose is to monitor the efficiency of the catalytic converter and, if the upstream O2 sensor is malfunctioning, take over for it. Your gas mileage should not have dropped with a bad rear O2 sensor.

[netwreck94]

Are there any air intake leaks? You say you replaced it with an OEM part - was this the $442 Pathfinder MAF, or the $89 Maxima MAF?

P0140 is inconsequential to the operation of your engine. It's a rear O2 sensor - its only purpose is to monitor the efficiency of the catalytic converter and, if the upstream O2 sensor is malfunctioning, take over for it. Your gas mileage should not have dropped with a bad rear O2 sensor.

I bought this one from Ebay

http://www.ebay.com/itm/Nissan-Pathfind ... 3cb74994fa

which claims to be OEM, for $50 with free shipping I figured I couldn't lose...but now who knows. I'm unsure about the air intake leak, I certainly don't hear any odd hissing or the like coming from that area but in all honesty I wouldn't know how to check. I had read what you just mentioned about the rear o2 not effecting operation, which makes me worry that it is indeed the MAF. However, I also read that the car should run somewhat better if you unplug the MAF which mine made no difference at all. I certainly do appreciate your quick response...just extremely perplexed at what to do. I could pay $25 for overnight shipping on another one of those MAFs which I got the seller to agree to replace if the one I send back does indeed prove to be bad.

Thanks Again

Evan

[Towncivilian]

$50 for an OEM MAF seems too cheap IMO.

Just ensure the hose clamps on the throttle body end and airbox end are tight, verify that you can't move the intake tube significantly, and that you don't see any visible gaps between any plumbing.

You can try cleaning the MAF sensor. Be sure to use proper MAF cleaner. You can try following the diagnostics on page EC-155 of the factory service manual. Failing that, I'd just buy an OEM Maxima MAF for $90 + shipping (I'm sure overnight is available if you need it now). While it's a Maxima MAF, many members here have used it without issue and it certainly beats the ridiculously priced and identical $442 Pathfinder MAF.

With an unplugged MAF, the engine will still not be able to achieve RPMs over 2400. The fail safe condition would be exactly the same whether the MAF is plugged in but malfunctioning, or unplugged altogether.