P0420 Code at 84k Miles

[calmb4dastorm]

So... I understand that there are other posts on here about the P0420 code (low CAT efficiency), however, I wonder if my situation might be unique some.

The only engine related mods are a 2.5inch straight pipe exhaust from the 2nd CAT back and a DDMWorks Short Ram (new k&n filter maybe 5k miles before issues)

Timeline:

About a month ago at 81k miles I had some warranty repairs done on my 2014 1.4L. Axel boots and oil pan gasket. The day I got it back I could hear a distinctive metallic noise when under load (accelerating harder than a cruse but not flooring it) but ignored it due to "trusting" the dealer.

2 days after the repairs I get a P0430 CEL. Cleared it and was good for a week before it came back. Cleared again and another week goes by before the CEL came back. Now it won't clear.

Yesterday, I take car top the dealer for diagnostics. Today they say that the CAT is bad and they will not do anything more than replace CAT for $738 plus tax and that the exhaust/intake are the cause. This seems odd since I've had both for 60k and 50k respectively. Also, the odd metallic noise, they say that it is the intake but it had never been there before.

My reason for posting here is to get some more experienced/expert input from you guys if possible.

Thank you in advance

 

[diazmjd]

That's crazy. I have a cat I could ship you for pretty cheap. Or you could buy a BNR downpipe, of course that won't fix the code without a tune. =)

 

[calmb4dastorm]

Is it CA "legal"? I forgot to mention that I'm in Cali

 

[diazmjd]

Is it CA "legal"? I forgot to mention that I'm in Cali

It's stock.

 

[Stew]

Code 420 huh? The dealer I'm sure removed the exhaust to R&R the oil pan, have you gone under the car to see if anything around the downpipe area seems obviously not right?

 

[calmb4dastorm]

It's stock.

yes. I didn't want to mess with it.

Code 420 huh? The dealer I'm sure removed the exhaust to R&R the oil pan, have you gone under the car to see if anything around the downpipe area seems obviously not right? .

I did. Nothing looked "off". That was my first assumption seeing how close the initial issue was to when they worked on it.

It appears that I'm going to have to let them work on it since I can not find a CA legal CAT that isn't nearly as much as what they are charging.

 

[Mr.turner85]

If the dealer removed your exhaust to do your oil pan gasket there are really only 2 possibilities as to it being relative to the code now. First is if there was any issue getting the cat pipe off and they used a persuading tool to help removal or if they completely removed it and it was dropped hard on the ground. If the substrate on the inside was already beginning to fall apart then either of these things could have caused the substrate to become separated and cause the code. The issues with this are that most likely you were gonna get this code in the future they just might have accelerated the timeline and there is no real way to prove it now. It is possible if the exhaust was removed and reinstalled improperly or with old gaskets that aren't sealing if there is fresh air entering the exhaust stream prior to the downstream oxygen sensor this could skew the reading of the rear oxygen sensor thinking the cat is inefficient. There really is no way an intake and cat back can cause the cat to prematurely fail if you understand how a cat works. Convincing a dealer of this is a different story. If you look in your owners manual you should find that the EPA has mandated a 10 year 100k mile warranty on cat converters if i remember correctly so my recommendation is remove the intake and exhaust and take it to a different dealer


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[calmb4dastorm]

If the dealer removed your exhaust to do your oil pan gasket there are really only 2 possibilities as to it being relative to the code now. First is if there was any issue getting the cat pipe off and they used a persuading tool to help removal or if they completely removed it and it was dropped hard on the ground. If the substrate on the inside was already beginning to fall apart then either of these things could have caused the substrate to become separated and cause the code. The issues with this are that most likely you were gonna get this code in the future they just might have accelerated the timeline and there is no real way to prove it now. It is possible if the exhaust was removed and reinstalled improperly or with old gaskets that aren't sealing if there is fresh air entering the exhaust stream prior to the downstream oxygen sensor this could skew the reading of the rear oxygen sensor thinking the cat is inefficient. There really is no way an intake and cat back can cause the cat to prematurely fail if you understand how a cat works. Convincing a dealer of this is a different story. If you look in your owners manual you should find that the EPA has mandated a 10 year 100k mile warranty on cat converters if i remember correctly so my recommendation is remove the intake and exhaust and take it to a different dealer


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Just visited with my exhaust guy. He says the same thing about the exhaust and intake. Unfortunately, California won't allow him to order it or work on it. The car is only 3 years old. I also looked up the California CAT warranty and it ends at 80K mikes. So it looks like I'm sol. As of right now, the Dealer is going to charge me $600 or so just to get the part (includes $100 "core"). Was told by the Dealer to call GM directly to try to strike a deal as a loyal Chevy Owner. This is my 5th Chevy (if you include my Geo) and 2nd Sonic. If that doesn't work... I'm half tempted to try something... Unsavory.