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I got this code the other day. It says that the O2 sensor didn't respond quickly enough. I said "Oh well so I have an O2 sensor that was slow one time" and blew it off.
 

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2007 Accord EX-L 4D 5MT
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Hey Rookie, it's now been 2 1/2 years. Did you ever get that code again after the OEM install?
I get the P0139 code about every other month. It will stay on for a day or two and then go away on it's own.
Same. It's been a year since I put in a Denso aftermarket O2 sensor and now getting random P0139. I replaced the upstream A/F with aftermarket Denso the year before, no issues since. I constantly check my trims with Torque and trims are always good, usually less than +5/-5 long term, and less than +10/-10 short term. I've found a pattern though. I have the 5MT. If I drive it "nicely", as in keeping revs under 5k, the CEL will go out and stay out after 3 cycles. But if I get over 5k rpm a couple of times the P0139 comes back.

2007 K24, 5MT, 197k miles. Completely stock, proper Iridium NGK plugs, original coils. Have already cleaned the MAF, which is one of the other potential causes of P0139 according to internet 'experts'. I have not replaced the PCV jet, but have checked it and it seems to be good. I may replace it soon just because it seems to be the original one.

I have a few theories:
1) There is probably a little oil burning at the higher rpm. I have run Mobil 1 High Mileage in 5W20, changed every 5k, since I got it with 135k. It burns a quart in 3k miles. So I don't have a big oil burning issue but it is using a little, and there are zero leaks. Could burning a little oil at high rpm be causing the code?
2) It sounds like I may be getting a slight timing chain rattle. I've been down this road with my previous daily and it didn't end well, so I'm going to pull the valve cover (probably time for a new seal anyway) and check the chain slack/wear. One of the issues with a worn chain is that timing is off just a little, which may lead to incomplete combustion and therefore causing increased emissions. We don't have yearly emissions testing here, but it probably wouldn't hurt to find a shop with the gear to test emissions just because it is a good indicator of engine health.
3) Maybe the aftermarket Denso sensors just don't last more than a year even though they work correctly for a while. Even though Denso makes the OEM sensor it probably uses cheaper materials in the aftermarket ones, which is why they are cheaper.

Thoughts?
 

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Discussion Starter #25
Yo, OP, anybody home?
Sorry LOL I’m kind of confused I could swear that I replied!

In short, since installing the OEM sensor, I have not seen the code come back!


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