P0420 Code - 140,000 miles - 2016 Silverado 5.3

[fondupot]

Hey all, my work truck is approaching 140,000 miles. Over the past few weeks I've had an engine light popping up for a few days at a time, then going away for a few days. I had the code checked and it was a P0420 - Catalyst System Low Efficiency Bank 1.

 

Now this truck has 140,000 miles. I think that's fair to say the cats are in need of replacement? Or Should I try replacing O2 sensors first and see if that corrects the problem. I've spoken to a few local shops and I get varying opinions and thoughts on how to proceed. Some say just replace the sensor. Others say replace just the cats. Another says just cut the old cats out and weld in universal ones. I am not sure what to think.

 

The truck does run "OK" it gets about 18-19 mpg on average, I do mostly highway driving in this vehicle. It does idle incredibly rough, but I know that is no uncommon for 2014+ trucks. Though, now looking back, that could be a symptom of a clogged cat...

 

Thoughts?

 

I had a couple shops quote me cat replacement and here are the prices they gave me.

 

Shop #1: ~ $900 - cut out old cats, weld in replacement universal cats, new sensors

Shop #2:  ~1,400 - replace cats only with OEM parts, no replacement of sensors

Shop # 3:  ~$2,100 - replace cats and sensors, with OEM parts

Dealership: $2,775 - replace cats and sensors, with OEM parts

[1SLOW1500]

If it was me I would just program those out. Or another option in o2 simulator, plug in like stock and just zip tie they up and away. Then thread in a block off bung in stock hole and done.
Or get a used low mileage y pipe.


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[Lsgun1]

If you want to keep the cats I'd get a whole Y pipe as well. In your state your exhaust hardware will probably not be rusted so it's easy to swap out yourself.

[Black02Silverado]

Does it use oil?  When was the last time you changed your plugs?

[fondupot]

58 minutes ago, 1SLOW1500 said:

If it was me I would just program those out. Or another option in o2 simulator, plug in like stock and just zip tie they up and away. Then thread in a block off bung in stock hole and done.
Or get a used low mileage y pipe.


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Eh. It's a company truck. For all intents and purposes its "my" truck, but the company pays the bills. I am just trying to do some diligence to figure out the best course of action. Because I will likely need to drive this truck to 200,000. The vehicle is registered in Ohio, and I think it will require emissions tests after 4 years. So that puts me into next year sometime.

 

38 minutes ago, Lsgun1 said:

If you want to keep the cats I'd get a whole Y pipe as well. In your state your exhaust hardware will probably not be rusted so it's easy to swap out yourself.

Yea, being that the truck is registered in Ohio, I think I need to keep the cats on it. It's also a company vehicle. My company bought the truck with 36k miles on it in Ohio, then it spent most of it's life in the southeast. now sure what condition the exhaust will be in under there, I haven't gotten under to look at it.

 

16 minutes ago, Black02Silverado said:

Does it use oil?  When was the last time you changed your plugs?

As far as I can tell, it doesn't use any oil. I had the plugs changed at 122k, when the vehicle was given to me. It idled rough before the new plugs. Virtually no change after the new plugs, still rough idle. I can feel the whole truck vibrate when in gear, goes away a little bit when in Park and Neutral. If I elevate the RPM's to 700, it smooths right out. I think the rough idle feeling is more like the engine mount TSB that was common on the 2014+ trucks. But I don't know if this truck ever had that TSB taken care of, and it's well out of warranty now, so I never bothered.

 

I've given it regular oil changes since then about every 6500 miles. I check it a few times between oil changes and never seen the oil level drop.

[Doublebase]

Spoiler

With a catalyst efficiency code I'd probably test the O2 sensor first and or replace. That code means that the cat isn't efficient in regards to what the rear O2 sensor is telling the computer, so it could very well just be a bad sensor (that would be the cheapest and easiest option, also the first option). Your rough idle could mean a couple things, but a failed rear O2 sensor wouldn't be one of them - the rear sensor should not effect drive-ability - but I do wonder if perhaps you have some carbon buildup on those valves...maybe even enough has fallen off and clogged or damaged the cat? Cats generally are good for the life of the vehicle unless they're damaged by raw fuel from a misfire, a coolant leak into the combustion chamber, burning a ton of oil or even induction cleanings.  

 

Edited October 12, 2019 by Doublebase

[mikedeezxxx]

Change the O2 sensors first. That is cheapest first attempt. Most likely bad cats. Cat replacement is expensive.


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[CamGTP]

Cheaper yet would be to just flip flop the rear sensors. If the code still comes back as the P0420 with the sensors switched, then it's still that cat. It only costs you time and not $50 for a sensor you didn't need.

[fondupot]

I had a shop do a diagnostic. They did some tests with intake and exhaust pressure and also temps before and after cats. Came back saying cats are very clogged.

 

So I am having new cats and new sensors installed. Should have the truck back today.

 

Cost is going to be around 2200 out the door. Luckily, I will get reimbursed 100% from my company for this.

[Black02Silverado]

41 minutes ago, fondupot said:

I had a shop do a diagnostic. They did some tests with intake and exhaust pressure and also temps before and after cats. Came back saying cats are very clogged.

 

So I am having new cats and new sensors installed. Should have the truck back today.

 

Cost is going to be around 2200 out the door. Luckily, I will get reimbursed 100% from my company for this.

Keep us posted as to how it runs after you get it back.  For the CAT's to be clogged, something isn't making sense.  Unless you have been running contaminated fuel.  Massive oil usage would do it as well but you said it doesn't use oil.

[njk4o5]

ive put 160,000 on my corolla with the p0420 lit up the whole time. p0420 was designed by car manufacturers and implemented by the government to make you want to purchase a new vehicle its a complete joke

[fondupot]

8 hours ago, Black02Silverado said:

Keep us posted as to how it runs after you get it back.  For the CAT's to be clogged, something isn't making sense.  Unless you have been running contaminated fuel.  Massive oil usage would do it as well but you said it doesn't use oil.

 

It's very possible the truck was running crappy fuel for the majority of its life. It was a coworkers truck in rural Georgia since new. I have no idea what kind of gas he was using. For the last 20k miles I have been sticking to top tier stations (Shell, Exxon, BP, etc.).

 

The one thing this truck does when it gets warm and been running for a while, it idles extremely rough, and the whole truck vibrates erratically. I wonder if that was a symptom of clogged cats....who knows.

 

I should get the truck back tomorrow sometime. I'll report back.