Downstream O2 Sensors Replacement
 

For the first time I got a CEL light and code on my 2009, stock, non-tracked, 77K mile car. It is the downstream O2 sensor over volt >20 seconds: P0138.
Always used top tier super. No rattles, no power loss, normal gas milage, nothing that gets my attention in any other way. I cleared the code and went for another short drive a few hours later. After about 5 minutes the code reappeared. No other codes.
I am waiting for things to cool down a bit before taking a closer look but since the code took a few minutes to pop up again, I tend to think it is not a wiring issue.
I am spring loaded to just order a new sensor and install. Rock Auto has several. Walker, Denso, NTK, and Bosch are the four I would go for. The OEM one on several Honda Part Sites are all around $360 plus shipping. Ouch.
What are the better choices here in your opinion?
I also notice Billman recommends using a spark plug spacer to keep the tip intact from debris from the CAT. What are the chances I have stuff coming out of the CAT? If I add spacers, use just one?
Thanks.


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Your current O2 may not be the issue.

Why is it reading high voltage? Is the CAT failing?

You can try spacing out your current O2 sensor. Use a 90 degree spacer and point the opening where the O2 screws in toward the front of the car.

If the code persists, it might be a lazy O2 sensor.

Replace with NTK only. I am using the Rockauto sourced NTK on my MY07 and its been working fine.

If the code disappears, then you may have a bad CAT. Just leave the spacer in and do nothing. Or replace the CAT.

I have never had a CAT go bad south of 200K miles on any car of mine. This is 77K with decent gas always. California blended top tier ($$$$) no less. No tracking. No mods. No flashpro. I performed a second valve check 10K miles ago and the plugs looked very clean.

Getting deeper in the manual, for the first time, it talks about resetting the ECM after clearing the DSTs. I have not done that. I have also not created the jump wire to test the voltage.

Note: I have the 2009 second edition book (final book from Honda) but on this section there is no inclusion of the 05-09 model. It is just the 05.



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Cosmo, I had my secondary O2 sensor go bad at around 42K. Pretty sure the previous owner used good gas. I could reset the CEL, but the light would just keep going off after a few miles. I also replaced the primary sensor (that one is a pain in the ass to replace). Our AP2 use two different sensors for front and back.


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Front (primary) sensor. Part number: 36531-PZX-013.


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Rear (secondary) sensor. Part number: 36532-PZX-004

I reset the ECU and the warning light has never come on, again. :)

Thanks. I notice that the usual recommendation is to replace a pair of sensors (2 downstream OR 2 upstream if the car is so equipped) but our S2000 has only one up and one downstream. (That is why you get the additional detail of right or left "bank". On a V8 or V6 or transverse engine that can be important) Did you just want to cut things off at the pass?

Did you add the spark plug spacers on the downstream one a la Billman?

Frankly, I am not sure about the term spacers. Are not those simply the crush or rotating washers that come with every spark plug? B Serious said to get a 90 degree spacer to adjust the orientation. Where the hell do you get that? Never heard of that before.

No, I did not add a spacer. I am not familiar with 90-degree spacers. The O2 sensors were changed about 4 years ago. No problems. My cat is doing fine...meow!!!

The secondary O2 is easy to replace. I used Loctite copper anti-seize paste on the threads. Primary is in a tight spot, especially the loom wiring . This video helps explain the mess. Skip to 3:20 (I hate how these DIY videos HAVE to have 2 minutes of some knucklehead explaining life's mysteries and all the ppl he's hip with). ;)

I found this on a video online about CAT and secondary O2 replacement. You can clearly see from the 2 screenshots how the honeycomb material moved aft and impacted the sensor causing the fault.
I am not sure how a spacer is going to prevent contact between the honeycomb material and the end of the sensor protruding into the CAT itself.
Can someone help me out here?


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Cos,
I don't know what thread our o2 sensor is but here is a 90* spacer
https://supremesuspensions.com/produ...iABEgKlY_D_BwE

The spacer goes into the cat and the o2 screws into the other end keeping the o2 sensor away from the honeycomb.

Rod

Cos,
I don't mess with the up-stream O2 unless my gas mileage is going south. The rear O2 just tells the ECU that the cat is working, does nothing for gas mileage. That O2 spacer will not pass SMOG "if" they see it. Never put a spacer on the up-stream O2, you want that one to sniff the exhaust to keep your fuel mixture right(not to lean, not to rich).

Rod

the 90 degree thingy on my test pipe is an angled spacer.

Spacers also come in straight flavors. Its a spark plug defouler that is used to move the O2 sensor outside of the exhaust stream to fool it into thinking everything is fine.

You will not pass a visual inspection, however. So this likely won't work in CA.

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Here's a spacer set that comes with a straight and angled configuration.

https://motorgenic.com/o2-oxygen-spa...BoCYsQQAvD_BwE