P0171 O2 Sensor 1 or Sensor 2?

[Illume]

Hey guys,

2000 RX300 and long story short, I have been clearing a bunch of codes by replacing things like knock censor, MAF sensor, coils in order to be able to pass emissions test.

I have one code left, P0171. I know this is typically the MAF, but since I just put a new one in, I can only think of the O2 sensors that are left.

Of the Bank 1 sensors, is one more common to fail than the other? Is there any way to tell which one needs replacement? Or do I do whichever is easier and cross my fingers?

 

Thanks in advance.

[Ryan2020]

It is sensor 1bank 1.  Bank 1 is closer to passengers.  (Bank 2 is closer to front of vehicle). There are 3 total “oxygen” sensors.   Two are pre cat. Literally speaking, the 2 pre cat ones are called”A/F” or air/ fuel sensors but it’s not uncommon to hear them called oxygen sensors and everyone knows what that means.  The third one is post cat.  

 

The Bank 1 sensor itself is  accessible from under the car.  The wire connector connects just underneath the Intake manifold (on the right from above).  It can be reached from above or below.