Check engine light came on; Code P0420, any help

[rav3]

As the Title says, my Check engine light came on today on my 2017 Silverado 5.3L 4x4 with 31K miles. I checked the code & in came up, P0420 CHEVROLET - Catalyst System Low Efficiency Bank 1
I read this could be several items/issues. Guess I'll take it to the dealer & see what's up. Is there a common issue for this?

Has anyone had this come up & have a good solution.  

 

 

 

[CamGTP]

Means the drvier side cat is likely bad. The solution is replacing the y-pipe with new cats.

 

If you have a warranty, that should be covered I believe.

[rav3]

35 minutes ago, CamGTP said:

Means the drvier side cat is likely bad. The solution is replacing the y-pipe with new cats.

 

If you have a warranty, that should be covered I believe.

What would cause this with only 31K miles? Would there be any noticeable driving/running issues from this?

[CamGTP]

Stuff happens, cat converters fail when they want too or they fail because of a poor running engine.

 

Unlikely this engine has major problems burning coolant, oil or has had tons of raw fuel dump right into the exhaust while running.

 

It's a mass produced part and things can fail. Only if the cat is clogged up will it change how it runs because it can no longer breath out the exhaust.

[Ravenkeeper]

I just went through this with our '14 Cruze.  I replaced the Upstream O2, couple weeks later the Downstream O2, and about month after that, the Catalytic Converter and Upstream O2.  It's been about a month since replacing the CC/O2, no recurrences.

[WilliamBos]

On 5/11/2020 at 5:29 PM, rav3 said:

As the Title says, my Check engine light came on today on my 2017 Silverado 5.3L 4x4 with 31K miles. I checked the code & in came up, P0420 CHEVROLET - Catalyst System Low Efficiency Bank 1
I read this could be several items/issues. Guess I'll take it to the dealer & see what's up. Is there a common issue for this?

Has anyone had this come up & have a good solution.  

 

 

 

Bad O2 sensor upstream(Sensor 1).  Emissions warranty should cover it.

[rav3]

12 minutes ago, WilliamBos said:

Bad O2 sensor upstream(Sensor 1).  Emissions warranty should cover it.

Thanks for info Will. However I checked their voltage output & they are functioning correctly.

[CamGTP]

P0420 code is reported by the rear o2 sensor.

 

If the front sensor was bad or if something in front of the cat was happening the front o2 sensor would be throwing other codes to show this. Like a lean or rich code, low voltage code or heater circuit.

[Colossus]

A good diagnosis will determine what is wrong instead of just throwing parts at it.  Just because a code comes on for the catalyst or Oxygen Sensor doesn't mean you go ahead and replace those things.  You find out WHY the light came on first.  Things up stream can cause an O2 sensor or other code to be thrown. 

Edited May 14, 2020 by Colossus

[rav3]

P0420 UPDATE: Dropped the truck off at the Chevy dealer this morning and just received a call from the service writer; He says it needs new cats; they will have to order them as they do not stock them & it will take about 4-5 days to get in. I can pick the truck back up & drive it until the parts come in. He said it wouldn't hurt the truck. Is this a good statement? BTW, all covered by the warranty. I knew that but glad to hear those words as at dealer costs, as I figure it, will cost about $1300 in parts & probable 2 hours labor ($250-$300) = $1700 including tax.

[davester]

Wow, that's fairly unusual for a vehicle with that low mileage on it.  Once you get it back, you might want to check the fuel trims for both banks, to see if one side is worse than the other (as in, if one banks isn't working quite right, and using more fuel, that can damage one of the cat's over time, but the problem may not be bad enough to cause other engine codes to appear.

[rav3]

Picked it up this evening since it'll be next week before parts come in. Again, the service advisor said it wouldn't hurt anything. When i started it up the 'check engine light' was off. I guess they cleared the code. Drove home & not light came up on the cluster. You'd think if the cat(s) where bad they'd trip the check engine light again. Strang. I would of thought GM would have them clear the code & see if it came back before replacing the cats @ $1300 part. That's ok. At least I'll have brand new cats.

[Colossus]

Make sure you are using top tier fuel only as well. 

[bill cruz]

Having the same problem with a 2009 silverado 5.3L,just replace all O2 sensors and  a day or two later got a p0420 on bank 1 ,under warranty but with 160,000 miles  I will probably replace the whole wye,bought the truck used  looks good and I like it but we all know that things go bump in the night.

[rav3]

I thought I'd post an update. The dealer finally got the part in, the Y  pipe, and installed it in 2-3 hours. No more check engine light. All is good. FYI, that's one reason I bought a "Certified" truck. I know this would be covered by emissions warranty but even better with 12 month/12,000 miles bumper to bumper coverage, so no hassle & even get a loaner.