oxygen senser how to replace??accent 2000

hyundai 2000 accent.im buying a part on friday.its a oxygen sensor i got the engine code po422.main catalyst effeiency blew threshold (bank1).my question is do i buy the top o2 sensor or the bottom o2 sensor??first
time replaceing o2 senser.do you have to disconncet battries?to replace o2 senser? thank you
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If you received a code p0422, it's more likely you have a catalytic converter problem.
You should replace any oxygen sensor that's having a problem. You won't need to disconnect the battery, just have the car off. You unplug the sensor, and unscrew it from the manifold or exhaust pipe, depending on the sensor being replaced.
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