Nissan Repair: O2 Sensor Location, air fuel ratio, oxygen sensors

Question
I have a P0139 Heated Oxygen sensor - bank 1, sensor 2 on my 2001 Nissan Pathfinder 3.5L V6.  I am sure this is the post converter O2 sensor, but is bank 1 the left or right side, looking at the front of the vehicle?

Answer
Brad, this is from http://www.nissanforums.com/pathfinder/142402-01-pathfinder-le3-5-ses-po139.html

Also, bank one is on the side where the number one plug is.  It is shown in the owners manual.  I would replace all oxygen sensors at once.  I did this last year to my 2000 Maxima.  I was being cheap and replaced one and a couple of weeks later the other one did the same thing.  The get coated with contaminates and need to be replaced.  But, on yours there are technical service bulletins listed below.  Warranty is probably over but you could check with your dealer...

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.