Oxygen Sensor Part Numbers and Locations?

[stevencox93]

So im getting ready to sell my Xterra since I have way too many vehicles now and just bought my truck. Problem is I have an engine light on and knew it was an O2 sensor and was gonna fix it before I sold the X since Im a honest guy well come to find out its all 4 sensors!! So what are the part numbers and how hard is it to do myself in replacing them?

 

[Muadeeb]

Sensor 1 is dirt simple; just reach on from the engine bay. 2 is a little more annoying, as you likely will need to get to it from below. RockAuto will have all four, and I think Bosch is the OE sensor

Edit: just out of curiosity, what are the codes?

 

[maillet282]

I replaced the upstream ones by going through the front fender liner. removed the liner and there it was no need to reach in the engin compartment

 

[stevencox93]

Cant remember the codes. there were 13 were they kept saying high voltage pending then a real code and all the codes pulled were for left side upstream and downstream and right side upstream and downstream. The left side ones were never replaced and the right side ones were replaced then have caused problems ever since but the dealership went under so Nissan wont warranty the part because I went over 3000 miles since they were installed after three weeks of having the work done.