I had purchased in 2020 new Denso A/F sensors to replace the Bosch ones.

I must say that my knowledge of systems in particular to emissions was very low and it could be stated that I was a parts changer, at that time.

These codes always seems to present a challenge, as you start to wonder if it's a vacuum issue, fuel distribution issue, air fuel sensor, catalytic, or an O2 sensor, etc,

So I had a P1274 code, A/F Ratio Bank 1 (Passenger side).

In any case I found the Nissan Service manual very good in checking the situation, and "proved" that the Bank 1 S1 A/F sensor was indeed faulty (there were internal resistance issues in the sensor) but not on the heater circuit, which is usually the main problem with them.

However, in my search on the subject, it seems there are a lot videos on the subject, so much so, that it winds up being a bit confusing.

I'm not sure if anyone is familiar with DiagnoseDan youtube channel, but this German fella is very good at describing what should happen, and really created a definitive display to help people understand how all this works.

In his case: the BMW pointed to a Bank 1 Sensor 2 Lean Code, not an A/F ratio code on Bank 1, with misfires.
In mine: Nissan fired a P1274, Bank 1 Sensor 1 A/F code, no misfires.

I thought his video explaining it, makes a lot of sense. He has a number of good videos, and he's more an instructor in these. His short video is good.

https://www.youtube.com/watch?v=Dwij_fu ... iagnoseDan

I replaced the A/F sensor with confidence.
All the data across both banks match now, and the idle has smoothed out as my Bank 1 was starving for fuel.