If codes 0171 and 0174 indicate it may be O2 sensor, why are there no faulty O2 codes?

Question

Found on 2000 Nissan Sentra, 1.8l engine. No other codes displayed.

Answer 1

P0171 Lean bank 1

P0174 Lean bank 2

In this condition the 02 are reporting the condition of the engines fuel control, The ECM test the 02 condition before it code a lean or rich condition, What you need to look for is for false air such as vacuum leaks, especailly at the MAF (mass airflow ) air duct tube, incorrect fuel pressure can also cause this to code up,and the MAF sensor itself.