I have been searching but havent found alot. I have both a P0138 and P0319 codes so I know it is the bank one sensor 2 i believe. This is the first time I have gotten the check engine light on. Any one have to change out thier oxygen sensors? how do you know for sure? any info would be great.

 

Those codes mean there is a problem with the rear o2 sensor in bank 1. There is a TSB for reprograming the ECU and replacing both(bank 1 and bank 2) rear o2 sensors:

http://maxima.theowensfamily.com/tsb/NTB02-051a.pdf

The sensors are not covered but some have said the cost of reprograming the ECU is covered under the longer emissions warentee.

Hope that helps!