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P0430 - Needs a Catalytic Converter??

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P0430 - Needs a Catalytic Converter??

Postby thacounty [OP] » May 17 2017, 2:40am

My truck is throwing the dreaded P0430. Changed the 02 sensor and that didn't help. The code is back, so I'm guessing I need a new cat. Now I have a few questions...

What cat do I get? Is the OEM really $900????

What caused it to go bad? There are no misfires. I put new plugs and wires on at 115k. I don't want the new one to go bad, so how do I stop a problem that I had no idea existed?
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Re: P0430 - Needs a Catalytic Converter??

Postby thacounty [OP] » May 17 2017, 2:11pm

Anyone replaced a cat on their NNBS?
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Re: P0430 - Needs a Catalytic Converter??

Postby Alex_M » May 17 2017, 2:19pm

A shop can weld in universal replacements for MUCH cheaper than that unless you have to adhere to California emissions. If you take that route though, be sure to replace both. An aftermarket cat will have different flow properties and you want to make sure you have equal back pressure on both banks.

A lot can cause them to go bad. Does your truck burn oil like most NNBS trucks? There ya go. Running rich will also damage them and a few other things.
Last edited by Alex_M on May 17 2017, 2:23pm, edited 1 time in total.
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Re: P0430 - Needs a Catalytic Converter??

Postby ferraiolo1 » May 17 2017, 2:22pm

so expensive because you have 2 cats welded into your y-pipe, so the whole pipe has to be replaced if going back to factory. Unless you do what was said above.
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Re: P0430 - Needs a Catalytic Converter??

Postby thacounty [OP] » May 18 2017, 2:26pm

Thanks everyone. It absolutely burns oil so it looks like I'll be stuck with bad cats every once in a while. I will probably go the cheap route since I can't stop it, short of a rebuild. Also, it does run a little rich, but I thought they all did. Will I lose performance with high flow cats? Won't higher flow move my torque and the HP curve out to higher RPMs

Thank you both!
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Re: P0430 - Needs a Catalytic Converter??

Postby rollover » May 18 2017, 3:11pm

I am not an expert on this but if it is burning oil and that is what caused the cat to go bad doesn't that mean the other cat is soon to go bad also? In which case would it be cost beneficial to replace both at the same time from a labor stand point unless of course you are doing the work yourself? I have read that not using OEM cats can cause the downstream O2 sensors to not be happy and generate codes that will not go away. Not sure how accurate this is.
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Re: P0430 - Needs a Catalytic Converter??

Postby JoshInWV » May 18 2017, 4:03pm

No there's some truth to that. I'd keep the old cats and fix the problem before subjecting new cats to an old 'cat-killer' problem.
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Re: P0430 - Needs a Catalytic Converter??

Postby Alex_M » May 18 2017, 5:12pm

thacounty wrote:Thanks everyone. It absolutely burns oil so it looks like I'll be stuck with bad cats every once in a while. I will probably go the cheap route since I can't stop it, short of a rebuild. Also, it does run a little rich, but I thought they all did. Will I lose performance with high flow cats? Won't higher flow move my torque and the HP curve out to higher RPMs

Thank you both!


No. Its such a small change in overall exhaust restriction that you won't notice any difference.

How rich is a little rich? They all are tuned to run slightly rich because rich is better than lean (for the engine)and the cats can handle it to a point.

rollover wrote:I am not an expert on this but if it is burning oil and that is what caused the cat to go bad doesn't that mean the other cat is soon to go bad also? In which case would it be cost beneficial to replace both at the same time from a labor stand point unless of course you are doing the work yourself? I have read that not using OEM cats can cause the downstream O2 sensors to not be happy and generate codes that will not go away. Not sure how accurate this is.


You have to replace both at the same time anyway because you want to keep equal back pressure on both sides. Even minor changes have the opportunity to create added stress to the engine's rotating assembly.

On that note, it will depend on what aftermarket cat you get. Smaller less efficient cats will have that problem, but larger and more efficient cats shouldn't throw any codes.

JoshInWV wrote:No there's some truth to that. I'd keep the old cats and fix the problem before subjecting new cats to an old 'cat-killer' problem.


I wouldn't keep the old cats. Oil burning will cause the. To clog over time, eventually drastically decreasing power and generating a great deal of heat. I had one start glowing yellow one time and it started spitting cherries out the tailpipe. How long the new cats last will vary depending on how much oil it burns.
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Re: P0430 - Needs a Catalytic Converter??

Postby idrivea2005sierra » May 18 2017, 5:33pm

Alex_M wrote:A shop can weld in universal replacements for MUCH cheaper than that unless you have to adhere to California emissions. If you take that route though, be sure to replace both. An aftermarket cat will have different flow properties and you want to make sure you have equal back pressure on both banks.

A lot can cause them to go bad. Does your truck burn oil like most NNBS trucks? There ya go. Running rich will also damage them and a few other things.


California is only difficult because of the CARB number supposedly stamped on the cat, meaning it will only fail visual not performance. I went through this nonsense with my VW. Dealership wanted 1300$ for the cat not including labor. I spent some time on the phone and long story short all cats are 50 state cats but CA requires a stamp. They all function the same and produce the same numbers in a sniff test. I ended up finding a bolt in replacement for 150$, had it shipped to my brother in AZ and he shipped it to me in CA. Passed with flying colors.

Vehicles newer than 2000 are now OBD2 scan only. They just check the computer for codes and values. IF the OBD2 port tells the emissions computer the car is running correctly the car passes. This is the exploit VW was using for the diesels. It went into a mode where the OBD2 output was "within range" and told the computer as such.
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Re: P0430 - Needs a Catalytic Converter??

Postby grim jeeper » May 18 2017, 6:33pm

It may be a long shot but have you check with a dealer I know GM extended the warranty on some cats...Asking is free
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