I got 2 OBD II code readings, P0171 and P0140 on my 2000 Sentra?

the po171 says it a fuel injector system too lean on it,and the po140 is a rear ho2s heater on it,that could cause the other codes also on it,id try replacing the 0-2 sensor first sense you know that has to be done,it may take care of the other code also,the 171 says it s fuel injector too lean on it,all you can do is try and replace it and see,that's the meaning for the codes when i looked them up for the year of the car,good luck,double check this though to make sure,i could be wrong on this one,good luck.

Just going by the codes, it reads;

po140= sensor circuit no activity found. Bank one, sensor 2

po171= fuel trim too rich. Bank one

at least that what the code says.