P0161 Keeps reappearing after Sensor replaced.

[G35coupe2006]

I recently failed my vehicle inspection because the Engine light was on indicating trouble codes P0140 or (P0141) and P0161. The car failed because of emissions apparently. My pathfinder runs fine, no pollution or vibrations just the engine light on. I read the service manual to diagnose the error codes and address both codes by installing new oxygen sensors. BUT the engine light keeps coming on for P0161. I troubleshoot following the manual. I checked the harness, bought three different heated oxygen sensor brands (the last one from Nissan) and I am still getting the engine light turning on after resetting. I took it to a couple of shops to make sure I wasn't doing anything wrong and both told me now that it can be the ECM but they are not sure. So I went online and googled up my problem. I found a service bulletin NTB00006c that said there is a reprogram/update for my 1999.5 pathfinder's ECM that correct the engine light from reappearing when a new oxygen sensor is installed. So I finally went to the nissan dealer to get the upgrade done to the ECM and they told me they need to run their on $120 diagnostic test. I had no other option left so I told them to run it and told them everything else I had done. They came with a service bill for $2400 to change the main harness (a short somewhere) and they are still not sure if that will keep the engine light from coming on. AND they told me that my car was a 1999 pathfinder and not a 1999.5 pathfinder which the service bulletin was for.

So I am looking for anyone for has ran into this before with the engine light still reappearing after replacing the sensors with OEM ones and checking the harness connection as well.

And what vin number/serial numbers belong to the 1999.5 pathfinder because I believe I have a 1999.5. My pathfinder was the new body parts found on the 2000 to 2004 pathfinders and my pathfinder is a 1999.5 SE Limited Edition. Which I read somewhere indicates it is 1999.5. I don't have any documentation to back what I believe is right. I think the dealer doesn't want to perform the ECM upgrade because of fear of crapping the ECM out and they may be lying to be by saying I have a 1999 pathfinder.

Please help, I am completely frustrated with a simple error code not allowing me to pass vehicle inspection. So far I have spent $360 trying to erase the code and my car runs smoothly. I replace the oil/filter every 3k miles. I use synthetic oil and oem filters.

[Towncivilian]

You can provide your VIN and I can discern whether your Pathfinder is indeed a 1999.5 and covered by the TSB you refer to. However, the TSB title is is NTB01-048A - 1999-00 PATHFINDER; MIL ‘ON’ WITH REAR OXYGEN SENSOR DTC P0138-P0140 OR P0158-P0160 STORED and this may not solve your P0161 code as such. Do you currently have a P0140 code?

Welcome to NICO!

[G35coupe2006]

I did have the P0140 code but it went away after replacing it with an aftermarket sensor. I also failed to note that I swapped the RH and LH harnesses to see if it would produce a code for the other heated sensor and it failed to do so. It popped up again with the P0161 code indicating the bank 2 sensor was faulty. This got me thinking that it is the ECM not the harness or sensor. So that is why I I want to try the ECM upgrade. Is there diagnostic that can be performed on the ECM to see if it's good. How can I find out what firmware or version software my ECM is currently running?

[Slumpert]

I always thought the 1999.5 was just checked by looking at the date code on the door..

[Towncivilian]

It's not possible to know your ECM part number (effectively its firmware version) without having access to a CONSULT-II scan tool (dealer-only basically).

If you want, I can provide a link to the aforementioned TSB and you can print out a copy and ask your service adviser about it; perhaps he can see if the TSB is applicable to your VIN.