Which 02 sensor causes the cel?

[gearyr]

My cel is on. Have the P0420 code. Replaced the Bank 1, sensor 1 02 sensor in November. Which 02 sensor causes the cel light to come on? The upstream or the down stream 02 sensor? I bought 4 of the 02 extenders to try to fool the computer. So I can pass emissions testing. Need to know which 02 sensor to fool to get the cel off. This is on a 2010 Pro4X Xterra with 157,000 miles on it. Thanks

 

[Muadeeb]

0420 is the sensor after the cat on bank one. I believe that's still the passenger side on the gen 2.

 

[jsexton]

Secondary sensor. Bank 1 is passenger side. Bad sensor is rarely causes a p0420... usually a high/low voltage code when the sensor is bad. Almost always the cats when you get p0420/0430.