Duramax Code 0420

Lacy0923 · June 5, 2017

Hi Guys, I am a new Diesel owner and have a question. I have a 2013 GMC Denali with 110K miles. While driving the other day, I noticed the engine light came on. I panicked and stopped at a local parts store and they checked the codes, It pulled a 0420 "Catalyst System Efficiency Below Threshold (Bank 1)". I stopped by a shop and they said my catalytic converter was probably shot and needed replacing. I'm not one to drop thousands on a whim so I did a little research and the next day the check engine (idiot) light went off. So, my question is, was my truck in need of a regen and it took care of the problem itself? I am not ready to gut the exhaust and retune just yet, but I don't want to buy a new converter either. Especially if the problem has corrected itself. Thoughts or advise would be appreciated.

casey.mikl · June 5, 2017

Drive it around and see if the light comes back on at all. I definitely would not replace it with stock. I would delete the whole def system. And get a custom tune if the cat is bad.

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davester · June 5, 2017

You may want to see if it's still covered under warranty, as the cat should last longer than what it has...

Swimmer8366 · June 6, 2017

Drive it around and see if the light comes back on at all. I definitely would not replace it with stock. I would delete the whole def system. And get a custom tune if the cat is bad.

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I'm with you delete it all together. And custom tune the beast.

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casey.mikl · June 6, 2017

Or you could swap that diesel out with a good ol reliable 6.0, I'll trade ya ;) lol. That truck deleted with a tune will run like a raped ape.

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barry G · June 6, 2017

that code is terrible on the trucks..all the way back to 1996.

I have a 5liter gas, replaced a bad o2 sensor in front of the cat, and now it does not match the one in back of it..

nothing to do with cat, and have the 420 code random.

cat passes inspection by getting another check.

your state should have a separate inspection, to go against the code and verify the cat another way.

my locale does not even pay attention to it come inspection time.(420 code is not trusted)

Jsmith7535 · July 21, 2017

What is the warranty on a 2014 Denali emissions system? A guy is suggesting I also get rid of the cat system but my truck only has 46k - hate to do it prematurely and void warranty. Throwing codes like crazy!

Colossus · July 22, 2017

There is an extended emissions warranty on some of them. My 12 had it in which they replaced the DEF system and a few sensors. If they would have replaced the DPF under the warranty I would have been 100% satisfied! But they kept insisting there was nothing wrong with it. Even though 160 mile regens. Grrrrrr. You can call up your service department and give them your VIN and they can tell you.

Jsmith7535 · July 23, 2017

What is the warranty on a 2014 Denali emissions system? A guy is suggesting I also get rid of the cat system but my truck only has 46k - hate to do it prematurely and void warranty. Throwing codes like crazy!