I did an autocross yesterday (stock 06 S2000, 95k miles) with just 4 runs and when starting my car to leave, my CEL stayed on. I had the codes read and cleared but it came back almost immediately. I received the codes listed out below:

- P0138 - Oxygen sensor high voltage, bank 1, sensor 2
- P0137 - Oxygen sensor low voltage, bank 1, sensor 2

I'm wondering if it is the cat or O2 sensor. I don't hear any rattling from the cat to indicate that the innards have fallen apart. I'm a bit confused that the sensor has both high and low voltage. Anyone have experience with this? I'm wondering if I should begin tracking down a cat or just replacing the O2 sensor. I'd appreciate anyone's input that has experience with these codes.

 

I would just replace the O2 sensor... they're cheap vs a cat even aftermarket. They go bad, it happens.

 

OEM DENSO secondary O2 sensor is $300+ dollars. There is a Walker unit available for < $100. I usually go OEM but for less than 1/3 the price, I may consider. Does anyone have experience with a Walker O2 sensor? I'm also a bit concerned that if my cat is bad, it could take out a new O2 sensor, meaning that I'd have to buy a cat and another new O2 sensor.

Just a few weeks ago, I saw a low miles, used cat on craigslist near me. I almost bought it as a spare but did not...

 

You can get some cheap O2 sensors off of Rockauto.
I'd go with the Denso or NTK

 

yea from honda its expensive...

just buy a denso with the same part number for like 50 bucks. the primary is like 90.

i doubt your cat is bad. the 2nd core should come loose and rattle before your cat core stops igniting

 

Thank you all for the help. Some reason, I thought I was seeing the same price for the DENSO direct unit as I was for Honda. I just looked it up again and grabbed one for $91 on Amazon. I did also make a deal for an OEM cat from a forum member. I'd like to have a backup while they're still available. I get the feeling that over the next couple of years it will get harder and harder to find parted out S2k's and good OEM parts.

 

Well, my cat ended up being bad. The 2nd core came loose and knocked into the O2 sensor. I was able to change it out with my OEM replacement. I'm going to look into securing the 2nd core and fixing the old cat to have as a backup. O2 and cat replaced, no more CEL!