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Old 02-21-2011, 09:36 PM   #1
70stroker
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po420 and po430

96 yukon, 4x4, 5.7l.

Its throwing a po420 and po430code. the po420 pops up about every 60 miles or so. the po430 just came up for the first time today. I know its cat efficiency low.

What are some possible causes?
Good starting test procedures?
Any common problems associated with these codes and trucks?

Thanks in advance
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Old 02-24-2011, 05:26 AM   #2
scotts62
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Re: po420 and po430

Anyone have an idea or need more info?
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Old 02-24-2011, 10:12 AM   #3
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Re: po420 and po430

Scott there is probably a list of PO codes already posted here somewhere. It might be helpful to make a sticky out of that. Just a suggestion.

I know the PO430 is "catylitic activity below threshold". It means the cat ain't doin as much as it should. It can be a cat just gone bad and it can be something upstream has caused it to go bad. Burning overly rich, burning oil and burning antifreeze can all cause a cat to go bad.
The 02 sensor behind the cat monitors the cat's activity only.
How well does the truck run upon cold startup and when warm? Strong smell of gas when cold? Down on power when warm?

I don't remember what the PO420 code is for.
Scott?
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Old 02-24-2011, 05:32 PM   #4
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Re: po420 and po430

Ya if you find it before me pm me and ill make it a sticky to put the the FAQ thread that is a sticky.

I dont remember much codes, its been a bit since i have played with code readers and kept up on all that.
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Old 02-24-2011, 06:13 PM   #5
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Re: po420 and po430

How does it idle and how does it run at wider throttle openings?
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Old 02-24-2011, 06:17 PM   #6
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Re: po420 and po430

P0420-Three-Way Catalyst System Low Efficiency Bank 1
P0430-Three-Way Catalyst System Low Efficiency Bank 2
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Old 02-24-2011, 08:15 PM   #7
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Re: po420 and po430

yes thats what the codes are, sorry i was a little tired when i first posted and just assumed everyone new what the codes where. Sorry it was my bad.

i have found out I have bad cats. Both rear o2s where crosscounting the same as the fronts, and they shouldnt, the job of the cats are to do away with any rich or what not mixtures and then the rear o2s should steady out and read a good mixture, well they were not.

After we do not have emissions testing I took the cats out and welded in pipe. I sold them at the scrap yard for 40 a piece, then spent 8 dollars and built my own o2 eliminators. Very simple to do, and the codes do not come on anymore.

Thanks for everyones help.
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Old 05-16-2011, 10:31 PM   #8
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Re: po420 and po430

just be ready for insufficient EGR flow codes in the future.

the #1 reason I see P0420 and P0430 is coolant leaking past the intake gaskets. coolant contains silicates. silicates create a coating on the converter substrate blocking it from performing the necessary chemical reactions. it doesn't take a large leak. a very small leak, even vapors, over an extended time will do this.
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Old 05-17-2011, 08:58 AM   #9
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Re: po420 and po430

GM had a cheesy catalyst media when they first started using Cats, but the media used now is pretty techno-savvy. Whereas the early ones were filled with a palladium-coated ceramic-type ball-shape, the later ones look like honeycomb and are fairly complex in their design. If you look at each end, you'd think that it is a straight-thru flow, but it isn't. The media isn't heavy, but stick it inside the shell and it gains weight.

Hope it all works out for you.
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