P0420 and Cold Weather

Joined
May 19, 2018
Messages
100
Location
CT
About 4 years ago, as the cold weather really set in up here in CT my 07 accord threw an P0420 code. I had was not due for my emissions test for another year and noticed no symptoms, so I let it ride. When the weather warmed up, the light turned itself off.

The next year at around the same time, it threw the P0420 code at me again, along with a code for a temp sensor for the cooling system. I had just passed my emissions test shortly before and didn't want to spend the $$ on cat at that time, so I replaced the coolant sensor in the lower part of the radiator and did a drain and fill of the coolant. Shortly after the CE light went out on its own again. I thought maybe the temp sensor was somehow responsible for the P0420 code too.

The next year, when the weather got cold again, what do you know, it threw the P0420 at me again. I let it ride, and again when the weather warmed up the light went off again on its own.

This year the light came on for the P0420 just after I received my emissions test notice at the beginning of December. I decided to try to wait it out, and about 2 weeks later the CE again went out on its own, so the next day I brought it for the test. When I was called up for my results, the guy at the desk said something odd happened, and then proceeded to tell me that I passed the test, but the system showed a P0420 code. He said he had never seen that before, as it should have failed with the code printed on the test result sheet, but not to worry because at the top of the page in bold it showed "passed" and that was all that mattered.

Then just today with overnight temps in the single digits, the light came back on for the P0420.

It has been about 4 years and close to 60k miles since the first time it threw the code. I am good for another 2 years at this point, but the light is annoying to look at and my code reader has never been able to clear this code. Just curious if anyone else has experienced anything similar?
 
My 07 Accord SE with a 2.4 did that also...I changed the rear o2 sensor and it took care of it... Get the oem one not a fit all one...
 
My 07 Accord SE with a 2.4 did that also...I changed the rear o2 sensor and it took care of it... Get the oem one not a fit all one...
Thanks, that's good to know. I was a little afraid to touch the sensors, as I have heard stories of it making them "more sensitive" and forcing replacement of the CAT after that.

Not sure how much truth there is to that though...
 
Thanks, that's good to know. I was a little afraid to touch the sensors, as I have heard stories of it making them "more sensitive" and forcing replacement of the CAT after that.

Not sure how much truth there is to that though...
If you look at the Accord sites you will see that this is a common problem on the older Accords...Mine started to do it around 120000. Changing the back o2 took care of it...Had the car till 386000 and the code never came back....
 
i am in Pa + very cold weather has similar on my 2011 fronty SV + a friend with a Titan had the codes BUT he had cats installed under warranty BUT stealer TRIED to bill him!!
 
My 2003 does much the same. The wife has been driving it now and we all know that they are great at ignoring lights on the dash, so I have yet to do anything about it!!
 
Sounds like a somewhat common problem for Hondas. Also sounds like the CAT is likely not the culprit, which is a good thing from a repair cost standpoint.

I think I'll probably wait it out until I am due for the next emission test and look into replacing or spacing the downstream sensor then if needed.

Thanks for all of the replies!
 
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