• The O2 B2S1 voltage is always double O2 B1S1 voltage.
  It follows that the Short Term Fuel trim on 2 is also double that of 1 but in the opposite direction of course.
  This makes bank 1 A/F look lean always, and bank 2 A/F rich always, in twice the proportion.
  The kicker is that when driving at about 40 mph, the voltage on B2S1 blips at 1.275v, and the STFT21% is 0% at that moment.
  Some explain this unusual voltage reading outside of 0-1v is
  • a) due to Nissan using narrow band O2 sensor (with range 0-1.275v) and
    b) 1.275v indicates a perfect 1.4:1 A/F ratio.
  There are no DTC codes since replacing two bad coils

VStar650CL wrote: ↑

Sun Dec 12, 2021 7:47 am

Engine needs to be fully warm and cats lit, at 2K RPM with no load the A/F's should both read between 1.37V~1.57V. Readings outside the range are usually from bad or inoperative heaters or heater circuits, so check the heater fuse and inspect for burnt/damaged wiring before condemning the sensors. Heat shield bolts on Bank2 have been known to fall out and can cause an exhaust leak that screws up the Bank2 readings and may melt insulation.