Are my AF ratio sensors lying to me?

Hi all, I’ve been a huge fan of Mr. Danner’s videos for a while & studying these forums has helped me a ton. I am very much appreciative of you all. More than just a “help me fix XYZ problem,” I’d really want to learn more of your methodology and which “direction” to turn to hone my diagnostic thinking.

So this is an ’05 Nissan 350z 3.5L V6 VQ35DE, 140k miles. Back story on this car: No MIL... But I’ve done extensive work on it recently & checked fuel trims to keep an eye on how it's running. I suppose this is more of a desire for optimization/prevention of a problem beginning/clarifying my confusion to help me get better.
From the FSM on the A/F ratio sensor: it's an air fuel ratio wideband sensor, not a standard O2 sensor. 6 wire Nerst cell, Nissan specs this as fluctuating around 1.5v at stoichiometric.
From studying videos + this forum about AF ratio sensors, this one appears to have a similar operation. It moves rich/lean in the opposite direction of ordinary O2 sensors. The generic OBDII data *should* report 0-1v. Per Snap On troubleshooter guidelines, the translated OBDII data being reported represents about 1/5th of the actual reading, (so .3v*5=1.5v). This sensor operates by amperage fluctuations to my understanding. I don’t have a microamp clamp, and I don’t believe I can scope this aspect of sensor performance via back probing.
Starting with the fuel trims, long term is still learning after a reset, but I saw bank 1 ST bouncing pretty high (20%+). In the graph, 0-5 minutes is slow driving with a warm engine, idling between minutes 4 and 5, then highway from 5 minutes onward with a bit of WOT.
I checked out A/F sensor reading and here’s where things get strange to me.
B1S1 = .3v (x 5 = 1.5v, which is in-line with desired according to the manual)
B2S1 = .6v (x 5 = 3.5v, higher/leaner compared to desired in the manual)
Also note that B2S1 looks like it’s clipping at 10 minute mark.

However, when comparing to fuel trims, it reads as if bank 1 is the leaner of the two banks, not bank 2 as I would expect.
From what I’ve read there are a lot of other Nissan owners whose AF ratio sensor specs line up with exactly what I’m reading. (B1S1=.3v, B2S1=.6v). Is this a weird Nissan quirk when transcribing current to OBDII generic voltage? I don’t have a Nissan Consult-II scanner to verify. I did a propane test during a cold idle (no change in idle) and a smoke test while engine was cold (no leaks visible).
So what would be your next "turn left or right" in direction
- In this situation am I right to lean away from MAF sensor since both banks see it?
- Should I search further with the AF sensor wiring to look for a shorted pump cell?
- Could it potentially be a leak in the balancing vacuum hose between banks while simultaneously having a dying B2S1 sensor?
- or hunt down something entirely different?
Also, what other PIDs would be most advantageous to look at while monitoring this? (I have the downstream data available too).
Thank you all for your collective wisdom and guidance in helping me grow more knowledgeable. I will post any more information that I find as well as fixes in this thread to help future readers.

-Respectfully, Dan
 

I found this video to be helpful in understanding Nissan O2 sensor behavior.

See if your scan tool shows a current flow and Lambda pid for the wideband sensors is what I would be looking for. If you do not have a check engine light on you might be chasing a problem that does not exist.

Thank you for this! Wouldn’t have guessed it from the title. Very much appreciated.

Unfortunately those don’t populate for me
I’ll see if I can find someone to run another scan tool on it. Thanks!

For future readers, I was able to hear from a jdm parts dealer, and this was his response:
“the offset ratio in the graph is indeed very weird and it's happened many times, but I'm not sure anyone has a real reason for it or done a proper FMEA on the sensors.typically this is fixed by replacing all four O2 sensors. this platform does not use pull-up resistors in the ECU, so any signal is read directly off the sensor including any fluctuations, noise, voltage offset, etc.  which may have led Nissan to the conclusion they needed to discriminate sensors via voltage offset.that would seem to be the case seeing as your top plot is very consistent and clearly reading out the AFR properly despite the signal voltage being different. if the sensors are not new, voltage offsets can drift as a result of age.in my case, [replacing only 1 sensor] did not help. the platform uses all four to calculate AFR for whatever reason, especially fuel trims. if you look at the sensor 2 readouts, it may show this.I run Nissan sensors only in my car because of the signal issues/ECU readout method mentioned before, and replace them either in pairs or as a full set.”

It’s about time that I replace them anyways..but I was just really curious about more of the behavior of these sensors—since I’m having difficulty finding it.