Another question about the P0171 code

[Power_Dr]

So here is my story, maybe some one can help.

I had the P0171 code on my 2001 QX4 and I have read all the topics about it. I tried to clean the MAF sensor and the code can back in about 3 days. I replaced the MAF and now about 5 days later the code is back on. Each time is says Bank 1 lean. I have a OBD II scanner with a program that can read live data. I logged the O2 sensor voltage and it looks like the Bank 1 sensor 2 is reading around 200mV and the reading is steady. The other sensors voltages fluctuate between 400-900mV. So does this mean that my rear bank 1 O2 sensor is bad or is it working but there is something else making it run lean.

Has anyone else read the voltage on their O2 sensors while they were driving, or reving the engine?

As I read about the P0171 a lot of people were able to clear it with just replacing the MAF.

Any help would be greatly appreciated.

Thanks in advance.