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I am diagnosing a lean condition, STFT is around 0-5%, LTFT is around 20-25%, BAS1 doesn't seem like it oscillating as much as it should, it says 3-3.5 volts which is where the specs says it should be, WOT it goes up to 4-5 volts but most the time its flat lined on the lean side. B1S2 works as should although i did have a heater circuit and p0420 before I had a battery reset. I did put an OEM equivalent last year.
The upstream AFR sensor voltage wont change much when the PCM is in fuel control.
High voltage is lean and low voltage is rich, so voltage going high under WOT is an indication of lean.
I usually reset the trims and look at fuel trim and the downstream O2 to determine if there is legit lean condition. If the computer is adding fuel but the downstream is reading rich, then the upstream AFR is usually missing reporting.
How are the fuel trims through the operating range of the engine?
BAS1 doesn't seem like it oscillating as much as it should, it says 3-3.5 volts which is where the specs says it should be, WOT it goes up to 4-5 volts but most the time its flat lined on the lean side.
Definitely a lean condition under load, like Noah mentioned. Your upstream air/fuel should be closer to 2.0V during power enrichment, not 4-5V. I've got some known good material in this thread for reference:
I'd be suspicious of an air measurement (underreporting MAF, unmetered air) or fuel delivery issue. What does Calculated Load (or Engine Load) do at WOT?
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