O2 Sensor question

[nos86]

Engine is throwing this code:

P0138 Secondary Heated Oxygen Sensor (Secondary HO2S) Circuit High Voltage

from what i understand there are two O2 sensors. Which one is this one and where is it located? Also where can i get a replacement one that is plug and play thanks.

Sorry if you've covered this before.

[get RIGHT]

I believe that is secondary. It is located under the caR, where your header and cat come together.

[Dave-ROR]

Engine is throwing this code:

P0138 Secondary Heated Oxygen Sensor (Secondary HO2S) Circuit High Voltage

from what i understand there are two O2 sensors. Which one is this one and where is it located? Also where can i get a replacement one that is plug and play thanks.

Sorry if you've covered this before.

The secondary O2 sensor is mounted after the cat, in the cat pipe that goes to the B-Pipe.

From front to back you have:
Header(or exhaust manifold+a-pipe), Primary O2S at the end of it, by the collector->Cat, Secondary O2S at the end of it, by the flange with the B-pipe->B-Pipe->Axle back muffler section.

however, this may not be a secondary O2S problem, the cat may be failing.

Try to reset the ECU and see if the code comes back, then determine if you want to replace the O2S, deal with the light or inspect further. If the cat is bad and you want to replace it, you'll end up going with an aftermarket high flow cat.

O2S plug and play = honda dealer, $180ish if I recall correctly.

[nos86]

i cleared the code but it came back a few days later
how do you know if it's the cat?