# 01 Pathfinder LE3.5, SES PO139 Help Please o2 sensor



## htyper96 (Apr 8, 2007)

Hello All, I have a 2001 Pathfinder LE3.5 with the SES light on. I have a scanner and pull codes PO139 o2 sensor ckt slow response bank 1 sensor 2, and PO138 o2 sensor circuit high vots bank 1 sensor 2. From researching, it is my understanding that there are 4 o2 sensors, 2 up front and 2 in the back and the error codes I am getting are for the rear, is that correct? Is there a way of pinpointing what rear sensor it is (maybe the bank 1 and sensor 2 thing) or do I just have to replace both of them. I looked all over the forum so hopefully this issue hasn't already been addressed. Any help would be very very apreciated.


----------



## 2001pathy_SE (Apr 9, 2006)

htyper96 said:


> Hello All, I have a 2001 Pathfinder LE3.5 with the SES light on. I have a scanner and pull codes PO139 o2 sensor ckt slow response bank 1 sensor 2, and PO138 o2 sensor circuit high vots bank 1 sensor 2. From researching, it is my understanding that there are 4 o2 sensors, 2 up front and 2 in the back and the error codes I am getting are for the rear, is that correct? Is there a way of pinpointing what rear sensor it is (maybe the bank 1 and sensor 2 thing) or do I just have to replace both of them. I looked all over the forum so hopefully this issue hasn't already been addressed. Any help would be very very apreciated.


can't give you an answer but welcome to the world of check engine light on a 01 pathfinder.


----------



## htyper96 (Apr 8, 2007)

2001pathy_SE said:


> can't give you an answer but welcome to the world of check engine light on a 01 pathfinder.


Seriously its starting to get rediculous, I have had this vehicle for about two years now and from the moment I owned it I have had SES issue. I finally broke down and bought a scanner, figured out from my short history of owning the vehicle it is a must to combat monthly engine lights.


----------



## 2001pathy_SE (Apr 9, 2006)

htyper96 said:


> Seriously its starting to get rediculous, I have had this vehicle for about two years now and from the moment I owned it I have had SES issue. I finally broke down and bought a scanner, figured out from my short history of owning the vehicle it is a must to combat monthly engine lights.


They have a software upgrade for our ecu i wonder if that will solve the issue.


----------



## michen00 (Jan 25, 2008)

I've been ignoring my P0158 (O2 high voltage, bank 2, sensor 2) for about a year now. I usually clear the code and it pops up a few months later. When I clear it, I check to make sure no other codes are logged or pending.

I can't remember where exactly I read this, but it seems the rear sensors are only for monitoring the health of the catalytic converter. The front sensors are the ones that are involved with running the engine. I figure there's nothing I need to know about the cat, since there's nothing you can do about it once it starts going bad (unless it's due to a problem upstream, and then there would be other codes and/or symptoms).

One downside of this strategy is I don't know if the SES light is coming on for another reason until I read the codes. The other downside is if the cat really is going bad, I won't find out until the next emissions test, and I would be unaware that I was polluting more than allowed.


----------



## smj999smj (Jan 1, 2006)

Nissan Technical Service Bulletin #NTB02-006 addresses the following codes for 2001 Pathfinders:

^ P0138 
^ P0139 
^ P0140 
^ P0158 
^ P0159 
^ P0160 

The bulletin states that if you have any of the codes, replace the incident O2 sensor. If you have codes P0138, P0139 or P0140, replace the rear RH O2 sensor with the following part, based on pro date:

Built up to 8/1/00: P/N: 226A0-4W001
Built on 8/2/00 or later: P/N: 226A0-4W010

If you have codes P0158, P0159 or P0160, replace the rear LH O2 sensor with the following part, based on pro date:

Built up to 8/1/00: P/N: 226A1-4W001
Built on 8/2/00 or later: P/N: 226A1-4W010

The TSB also has you check the ECM part number and compare to a list of ECM part numbers on the bulletin, which will require the use of a CONSULT II scantool (meaning a trip to your Nissan or Infinit dealer). Depending on the ECM program currently installed in your vehicle, it may need to be updated to the latest program revision. 

Rear O2 sensors are for testing catalytic converter efficiency and have no affect on drivability, unlike the front O2 sensors, which the ECM uses to help provide the proper air/fuel ratio.

As far as O2 sensor identification, "Bank 1" is the engine bank that starts with #1 cylinder. "Sensor 1" is the front or "upstream" sensor. "Sensor 2" is the rear or "downstream" sensor. Bank 1 on the VQ engine is the right side bank and Bank 2 is the left side bank. 

ECMs and ECM reprogramming is covered under the long term emissions warranty, often 7 years/70000 miles from date of purchase, so some Pathfinders MAY still be covered under warranty for this. The new ECM program has remapped parameters for the O2 sensor in regards to trigger an O2 sensor malfunction.


----------



## ebanc (Mar 1, 2008)

I have been getting the P0160 code on and off for a few months on my 2001 Pathfinder without any impacts on drivability, as you stated.

Yesterday, I had severe drivability problems (constant hesitation, stumble and very rough idle) with a flashing CEL. I only drove the car a short distance under this condition and then checked for a code afterwards. The only code that came up was P0160.

The strange thing is that now the car runs fine after sitting overnight.

Could the drivability issue be related to the O2 sensor in any way?


----------



## supraholic (Nov 21, 2005)

I had these problems as well.. after changing out both rear O2 sensors and reprogram by NISSAN fixed it all.. car would run fine/ no change in fuel consumption due to faulty secondary sensors.. its just that, you wont pass state emissions..


----------



## michen00 (Jan 25, 2008)

ebanc said:


> I have been getting the P0160 code on and off for a few months on my 2001 Pathfinder without any impacts on drivability, as you stated.
> 
> Yesterday, I had severe drivability problems (constant hesitation, stumble and very rough idle) with a flashing CEL. I only drove the car a short distance under this condition and then checked for a code afterwards. The only code that came up was P0160.
> 
> ...


The rear O2 sensors aren't supposed to affect driveability in any way, as per smj999smj's description of the TSB above.

I had the exact same situation as you: (constant hesitation, stumble and very rough idle & flashing CEL), drove less than a mile before checking for codes, and a long-term rear O2 sensor fault. Aside from the O2 sensor fault, I didn't get any trouble codes either. However, I did get a _pending_ trouble code for a #6 cylinder misfire. Make sure you check for pending codes.

I have since replaced my ignition coils to fix the misfire problem. (Search the forums if you don't already know about the VQ35 engine's ignition coil issue.)

I'm still living with the rear O2 fault.


----------



## htyper96 (Apr 8, 2007)

Hello again everyone and thank you for all your input to my post. I have some news to share that will hopefully help someone else out. I finally got around to dealing with my SES light (I hate seeing that on my dash board). I got under the old pPathy to locate the sensor and noticed a ground wire that seemed to come off my exhaust had broken. I re-grounded it, cleared my ecu codes and so far (its been 2 days) no SES light, cross your fingers for me, well that is untill the next SES issue.


----------



## TuffguyF4i (Nov 8, 2006)

I was having the same problems over and over again till i replaced my MAF. That seemed to cure all of my problems. No issues for 5k miles. 

I replaced the MAF with a maxima maf since it cost 150 less. Search for my thread for part numbers.


----------



## gajego (Jun 19, 2007)

htyper96 said:


> Hello again everyone and thank you for all your input to my post. I have some news to share that will hopefully help someone else out. I finally got around to dealing with my SES light (I hate seeing that on my dash board). I got under the old pPathy to locate the sensor and noticed a ground wire that seemed to come off my exhaust had broken. I re-grounded it, cleared my ecu codes and so far (its been 2 days) no SES light, cross your fingers for me, well that is untill the next SES issue.


Where are the O2 back sensors located? Around the engine exhaust? A schetch would be nice, as i would like to check the wires on mine.

Thanks


----------



## gajego (Jun 19, 2007)

Anyone care to respond?

thanks


----------



## michen00 (Jan 25, 2008)

gajego said:


> Where are the O2 back sensors located? Around the engine exhaust? A schetch would be nice, as i would like to check the wires on mine.
> 
> Thanks


The screen-shot below is from the Factory Service Manual for a 2001.0 year Pathfinder. It is page 9 of the FE section, which is for the 4WD Pathfinder. The rear oxygen sensors are parts 1 and 3. They are easy to spot from under the car, in the region of the front wheels.

BTW, you can get the FSM for free over at Pathfinder Service Manuals - Nissan Pathfinder Off-Road Association


----------



## gajego (Jun 19, 2007)

Thank You for the chart.


----------



## cmdmdq (May 31, 2008)

Hello all, I got the P0160 a couple of weeks ago but in my case I have noticed that fuel consumption went from the average 17mpg to 13mpg!!! on my first fill-up after I got the code. Do you think that replacing the Driver side (right?), after the cat. O2 sensor will solve the issue? 

01 Pathfinder LE 4x4, built bef. 08/00 with 21,000 miles (Yes, no kidding)

Thanks in advance for you help!!


----------



## lightimages (Mar 31, 2009)

*New part number?*



smj999smj said:


> If you have codes P0158, P0159 or P0160, replace the rear LH O2 sensor with the following part, based on pro date:
> 
> Built up to 8/1/00: P/N: 226A1-4W001
> Built on 8/2/00 or later: P/N: 226A1-4W010
> ...


Thanks for the original great post.

My PF has a March 2000 build date.
My local dealer says 226A1-4W001 has been replaced with 226A1-4W005.

Being paranoid, I called another nearby dealer and was told 226A1-4W001 has been replaced by 226A1-4W004.

(This kind of thing is how I came to be paranoid)

Which number is correct? 

Does the new part require a change in the ECM? 

ECM was flashed in late 2007 after a warranty converter change. Would that be current enough?


----------



## gajego (Jun 19, 2007)

I want to post a 1 year aniversary from last posted message. I am still driving with code 0160 and not replaced any O2 sensors. I do clear the code as soon as it appears, however my Pathfinder does not seem to be affected by this code, nor the gas consumption.


----------

