Threw a code p0140, O2 sensor 2 bank 1...the one after the main cat. Voltage was a constant 1.27 Reset the code and installed a new O2 sensor. Now it's reading a constant 0.31 volts, but not throwing a code. Is this throwing off the a/f ratio, and hurting performance or milage. Suggestions? Thanks.

 

that is just a secondary o2 sensor thats job is to monitor the cat. it has no bearing on a/f like the 2 primary o2 sensors do along with the maf. a/f is calculated by 2 primary o2 sensors & the maf except at wot when the maf works all by itself.