P0420 code goes away in warmer weather

[2010Civic]

I have a 2005 Honda Accord with the 4 cylinder. 185k miles. The last couple of months I've been getting the P0420 cat code, and occasionally a code for the O2 sensors but primarily the P0420 code.

In the last few weeks with the warmer weather I haven't gotten any codes. I'm in Minnesota so the highs are in the 40's now instead off well below freezing.

I wonder why this is? No way I'm buying a new cat for a 14 year old car so it's kinda nice the light went off.

 

[Leo99]

Might just be the upstream O2 sensor in the exhaust manifold.

 

[oldhp]

Sounds like you need to change the O2 sensors. 14yrs & 185K miles, setting codes. Change them out.

 

[slacktide_bitog]

You can get a new cat for under $80 on eBay, gaskets included

If you replace the cat, you should replace the oxygen sensors along with it. The oxygen sensors cost less than $50 for both of them.

 

[2010Civic]

I'm curious why temperature affects the problem. Not interested in buying a new cat and both sensors, especially cheap ebay stuff. The car is just my winter beater. It runs like a top.

 

[JTK]

Originally Posted by 2010Civic
I'm curious why temperature affects the problem. Not interested in buying a new cat and both sensors, especially cheap ebay stuff. The car is just my winter beater. It runs like a top.


Because in colder ambient temps, more fuel needs to be injected to compensate for colder, more dense air (more O2 molecules). It's possible your catalyst can't keep up with this.

 

[Revving2Redline]

Could just make a test pipe or seek aftermarket one. How do the plugs look?

 

[spasm3]

Originally Posted by JTK
Originally Posted by 2010Civic
I'm curious why temperature affects the problem. Not interested in buying a new cat and both sensors, especially cheap ebay stuff. The car is just my winter beater. It runs like a top.


Because in colder ambient temps, more fuel needs to be injected to compensate for colder, more dense air (more O2 molecules). It's possible your catalyst can't keep up with this.


+1

 

[Wolf359]

So why not just replace the upstream sensor? It might fix it enough so you can squeak by a little longer.

 

[14Accent]

Originally Posted by spasm3
Originally Posted by JTK
Originally Posted by 2010Civic
I'm curious why temperature affects the problem. Not interested in buying a new cat and both sensors, especially cheap ebay stuff. The car is just my winter beater. It runs like a top.


Because in colder ambient temps, more fuel needs to be injected to compensate for colder, more dense air (more O2 molecules). It's possible your catalyst can't keep up with this.


+1


+2 Richer exhaust = more work for the cat. At that mileage, it's tired. I really doubt the upstream sensor has much to do with it, it's probably just getting a bit lazy itself. Good thing there's no emissions testing here in MN. Clear the code and be on your way.

 

[slacktide_bitog]

Originally Posted by 2010Civic
I'm curious why temperature affects the problem. Not interested in buying a new cat and both sensors, especially cheap ebay stuff. The car is just my winter beater. It runs like a top.


Has your gas mileage gone down? How much longer do you plan on keeping the car?

 

[2010Civic]

Originally Posted by slacktide_bitog
Originally Posted by 2010Civic
I'm curious why temperature affects the problem. Not interested in buying a new cat and both sensors, especially cheap ebay stuff. The car is just my winter beater. It runs like a top.


Has your gas mileage gone down? How much longer do you plan on keeping the car?


Only slightly over the winter which is normal. -30F degrees actual air temp a couple days this winter.

Probably a few years. The car currently does not have a check engine light. I'm guessing the cat is just on the edge of tripping the light. It's not worth it to me to spend the money replacing the cat and sensors. Plus dealing with super rusty bolts. I don't care if the car is polluting a tiny bit more.

 

[KalapanaBlack]

Could just be a thermostat. If it's a Cali emissions Honda or Toyota from that era, the emissions are monitored VERY closely. I know many a GM CEL has been tripped by this. If the engine doesn't get to operating temperature within the factory specced timeframe, meaning the cat remains below efficiency for a longer than expected time, you get a CEL and a P0420. If you're gonna throw a part, throw a cheap part and see what happens.

 

[HowAboutThis]

My Honda dealer told me to clear the code with my code reader if it only pops on here and there when I owned an 02 Civic. They said if it starts happening more often or I notice idling or performance issues then they'd worry about it. OEM they quoted me about $1200 and they gave me a couple aftermarket brands that were decent given my car's age and mileage that would probably last ok that an exhaust shop could put on. The mechanic and service advisor were really helpful. Kind of shocked me.

 

[HowAboutThis]

Originally Posted by KalapanaBlack
Could just be a thermostat. If it's a Cali emissions Honda or Toyota from that era, the emissions are monitored VERY closely. I know many a GM CEL has been tripped by this. If the engine doesn't get to operating temperature within the factory specced timeframe, meaning the cat remains below efficiency for a longer than expected time, you get a CEL and a P0420. If you're gonna throw a part, throw a cheap part and see what happens.


This is what the Honda dealer told me, in terms of the emissions being super picky. They said usually it's first triggered and the car could care less, but the environmental regulations are so tight to meet spec.

 

[2010Civic]

As the temps are getting cold again the check engine light came back on for the cat and oxygen sensors. After installing a O2 sensor defouler a few days ago the CEL hasn't come back on. We'll see if it stays off but so far so good. Sure beats spending a bunch of money and fighting with rusty bolts!

 

[Andrew1972]

Clear the light drive on. This code had emitted since 2011 in my 07 MDX every 6-12 months. It goes away by the time I get sorted to deal with it.