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2014 Nissan Maxima - Very unusual case but I have to tell the backstory:
Owner states it all started when he returned from vacation (Sep 2023) and unknown person sabotaged (cut) his bank 2 upstream sensor and loosened the clamp on the rubber air tube near MAF. He butt spliced the sensor and shortly after started getting P0174 code.
He said he took it to a couple shops who said to change the sensor and he purchased a Denso from Autozone. Not fixed and second shop asked to get a dealership sensor which he did. 3rd shop said he needed a new ECM which he got from Flagship but the shop could not program it. He also stated that he was now getting a P0300 intermittently in December.
That's when he called me asking if I could source an ECM for him and install it. I agreed and the installation went well and programmed all 4 keys owner had. The only immediate issue I noticed is that the Air Volume Relearn would not complete despite meeting all conditions (stayed on executing forever).
During the test drive, the car was definitely misfiring with P0300 and P0150. I was puzzled but live data showed Bank 2 voltage at 1.2V and heater at 100% while Bank 1 was at 2.2V and heater around 25%. I installed the other sensor he had and the same issue. If I unplugged the sensor, the misfire went away and the car drove normally. I told him this might be a wiring issue and scheduled another session later in the week.
So today I checked continuity back to the ECM harness on the 2 signal wires and the ground wire and they were perfect. There was no short to ground or short to power on any of the 4 wires of the sensor harness. I had my head in a spin and couldn't understand what was in front of me. Started the car up and it was definitely misfiring again during a test drive.
For the hell of it, I installed the original sabotaged sensor and the car all of a sudden was Happy! No more misfire and the live data was showing 2.2V for both banks and heater at around 27% and guess what.......the Air Volume Relearn finally completed.
Can someone explain to me how can 2 Denso sensors cause a P0300? Resistance on the heater wires of both sensors were around 2.1 ohms. The owner states that he drove 30 miles afterwards with no check engine light. Tyler's AFR testing thread really was informative. Sorry....very sorry for this long post.
P.S. The only other issue is that the car needs a new a MAF sensor. The IAT was 40+ higher degree reporting and the MAF reading was a bit low.
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