O2 Sensor

My truck is throwing a code for O2 Sensor. Its a 06 V6 with 65K miles. How do I know which O2 sensor to replace? Thanks

 

The code is P0430
Catalyst system efficiency below threshold

 

Yea if I reset the code it will stay off for the next few drives. I hope its not the cats they are $$$ but at least in Florida their is no smog test

 

Is their a way to test the O2 sensors?

 

its the passenger side downstream. P0430 is bank 2. Bank 2 = cylinder 2 side

check for leaks before downstream 02 sensor. then if no leaks replace 02 sensor. then replace Air /fuel ( upstream sensor). if MIL doesnt go away, bad cat. also if there is bad (rotten egg smell from exhaust) smell from exhaust, its the cat. the only cat u have to worry about if there is no smog test is the manifold cat. 500$ for magnaflow direct fit manifold cat and 300-400$ for eastern direct fit manifold cat. Homework has been done.

 

Ometer test. test the electric waveforms based on factory service manual. Buy Ometer at wally world
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Oh and cats just dont magically go bad. Mecs say that to get more $ outta you. fixed my stuff 3 weeks ago with 02 sensrs, mecs said it was BOTH cats. so....

 

Thanks exhaust smells normal. Ill check for leaks in the A.M. and replace sensors accordingly