Working to track down P2A03, bank 2 sensor 1 check engine code. This code is signaling something is off with readings from the 1st O2 sensor sitting before the left catalytic converter. Replaced OEM (155K miles) O2 sensor with Denso (no change) then Bosch OEM (no change). Throughout we reviewed all exhaust parts to ensure no leaks. We also replaced mass air flow sensor with new OEM Hitachi for $35 off Ebay. Lastly went to clean out intake (found lots of grime) and saw that there were holes in the two corrugated rubber tubes on both sides of the intake duct. See images: https://photos.app.goo.gl/2yjzAvXXfzN7Ten6A... somewhat of a "duh" moment. Replacement rubber tubes are not available from Infiniti - the whole duct unit needs to be replaced. Got new for $205 (ugh) from dealer and replaced yesterday. There was an EBAY reseller making custom tubes (both) for $100 or so, but I skipped it. So, we will see if this does it. Of note, we did tape up the holes with electrical tape when we discovered it and the car seemed to run better in that window, but light did come back on after 200 miles. Let's see what happens with "real" solution. Next up in our brainstorming and research - is replacing?? downstream O2 (odd theory), ignition coils, fuel injectors?.. All weak ideas as we assume if there was an issue aligned to some of these ideas then there that a different code would appear. Another route is getting a Nissan scan tool to get more info than we have with our's. If you have any ideas or experiences, please let me know. One source of ideas was this - including last post on page 2 - https://www.clubfrontier.org/forums/f8/ ... de-61513/ . I will also update. THANKS Steve

Good triage Steve but if have gone for the cheaper Z-Tube intake instead of the OEM. Keep us posted though!

Ugh.. it is back after 75 miles or so. Thought we had it! I also should have mentioned in my original narrative that we ran some Techron and BG 44K through the gas tank during the troubleshooting process. Any ideas or suggestions on next steps would be appreciated. Of note, one key assumption we have is that this PA203 flagged issue is BEFORE the catalytic converter - any thoughts otherwise would also be appreciated. Thanks

my error.. typo - P2A03 is correct code

These are the things I'd look at
I have listed them in no particular order of importance. Do what's cheapest or nost accessible to you.

1. Intake leaks. You might need to do more than the electrical tape, as Ilya suggested.
2. Check the exhaust manifold for cracks or leaks. Bank 2 is the left side on the V6 (driver's side US).
3. Check the fuel injectors. Use an automotive stethoscope or substitute with a suitable solid object and listen that all 6 injectors sound similar.
4. What is the condition of your spark plugs? (Age, brand etc)

Thanks... Update..

Intake leaks. You might need to do more than the electrical tape, as Ilya suggested.
- We replaced the intake air mass meter"duct" ($200 OEM part with two rubbers flex ends on it). We also cleaned out carbon gunk from the upper intake.

Check the exhaust manifold for cracks or leaks. Bank 2 is the left side on the V6 (driver's side US).
- Discovered oddity via a mirror - bottom middle stud on driver's side exhaust manifold missing. Hmm.. Ugh. $$ if it is driving this.

Check the fuel injectors. Use an automotive stethoscope or substitute with a suitable solid object and listen that all 6 injectors sound similar.
- Have not checked, but prepared to replace injectors as cost is not bad ($70 for rebuilt Bosch OEM set).

What is the condition of your spark plugs? (Age, brand etc)
Brand new NGK Iridium IX installed in September.

ALSO .. (1) we discovered a tiny pinhole leak by a weld on the upper part of driver's side catalytic converter. We put some patch cement on it to see if it would make a difference. If it does, we will weld it. and (2) We replaced downstream driver's side O2 sensor. After some research we saw a possible correlation even though error code is only linked to upstream O2 sensor. Installed a direct fit Denso from Amazon for $74 (both driver's side O2 sensors are now direct fit Denso's which seems OK vs. OEM Bosch).

UPDATE: After patching hole and replacing downstream O2 - light came after two minutes of driving. Cleared and has been off for about 100 miles which is a good sign. We will see (and I will update). Steve

300 miles later (more than every gone without CEL on).. all clear. The downstream O2 sensor did not align to the codes, but it kept coming up in research and we chose to replace it. Obviously the pin hole was potentially a biggie. Not a perfect science "controlled" experiment to target a reason, but we're looking better.

CEL is now off... solved it.

Just had this code pop up on my M45