po430/420 codes

[Roy Goodwin]

I have an 07 yukon 5.3, just did an afm delete and while doing that I replaced all sensors and put new cats on. I put about 1500 miles on it and now I am getting a po430 and po420 code which is low catalyst. Was told to try o2 sensors on the downstream o2s but that didn’t do anything. Anyone have this problem before? Have done some research and haven’t come up with anything other then the spacers for the o2 sensors

 

[swathdiver]

I have an 07 yukon 5.3, just did an afm delete and while doing that I replaced all sensors and put new cats on. I put about 1500 miles on it and now I am getting a po430 and po420 code which is low catalyst. Was told to try o2 sensors on the downstream o2s but that didn’t do anything. Anyone have this problem before? Have done some research and haven’t come up with anything other then the spacers for the o2 sensors

Howdy Roy! Welcome! So are you normally running downstream O2 sensors? The upper and lower sensors are different part numbers and can be swapped side to side but not up and down. Unless they are loose or you have an exhaust leak letting air into the system it's probably the cats. Is the motor running well? What kind/brnd of cats did you use? I had a Chicom one on my truck fail within a year then put on a Magnaflow Y-Pipe with cats and all is good.

 

[Roy Goodwin]

They are AP Exhaust cats and y pipe, ordered them from rock auto. The correct o2s are in the correct spots and yes it is running downstream o2s. Everything got put back to during the afm delete. The motor seams to run fine other then losing about 2.5 mpg. A bad o2 crossed my mind at first then I got the codes for bank 1 and 2 catalyst low

 

[BG1988]

I have an 07 yukon 5.3, just did an afm delete and while doing that I replaced all sensors and put new cats on. I put about 1500 miles on it and now I am getting a po430 and po420 code which is low catalyst. Was told to try o2 sensors on the downstream o2s but that didn’t do anything. Anyone have this problem before? Have done some research and haven’t come up with anything other then the spacers for the o2 sensors

make sure the map sensor is reading correctly had a unplugged sensor tripping a P0430

if you lost 2.5MPG you are running rich and burned up the CAT P0420 (typically it's correct if you all ready replaced the sensors)..

i would check live data and see if the CAT is running about 500F to 600F typical idled warmed up...


if it's running any hotter (running rich) or if colder it's not working

they have a cheap reader that works with this at wal-mart it's only 40$ and will read the CAT temp..


If you do I suggest a GENUINE 100% OEM Equivalent Certified aftermarket and not a random converter you see online that claims to be compatible.


From AP Exhaust is the only 100% OEM Equivalent Certified

part numbers are


740566 Universal (weld on)
749233 direct fit;...

you could have a small exhaust leak as well you did replace the gaskets? with new ones

 

[Roy Goodwin]

All gaskets were replaced and only exhaust leak I have is at the y pipe flange after the cats and downstream o2s. The cats are only a few months old and don’t even have 2k miles on them yet. I will check the map sensor to see where it’s reading

 

[swathdiver]

They are AP Exhaust cats and y pipe, ordered them from rock auto. The correct o2s are in the correct spots and yes it is running downstream o2s. Everything got put back to during the afm delete. The motor seams to run fine other then losing about 2.5 mpg. A bad o2 crossed my mind at first then I got the codes for bank 1 and 2 catalyst low

If you erase the codes do they come back? If they got fouled with oil or fuel or something, sometimes this can be burned off by driving the truck in a lower gear at highway speeds for a spell. Break in period is usually the first 100 miles or so. If it keeps throwing codes, and you've lost gas mileage, chances are they are shot. Should be under warranty though.

 

[Roy Goodwin]

The code keeps coming back after being erased, the cats have a 5 year warranty on them but not sure how easy of a process it is to get them covered

 

[swathdiver]

The code keeps coming back after being erased, the cats have a 5 year warranty on them but not sure how easy of a process it is to get them covered

Well, unless the O2 sensors are loose and allowing air in, they are in need of replacement. Is your truck tuned and do you have to pass state inspections? My plan when these go is to gut them out and turn off the downstream sensors in the tune and be done with it. The Y-Pipe is really nice and flows better than stock.

 

[Roy Goodwin]

I have a diablo tuner set on 87 econo tune and to disable the afm. 02s are tight, the cats are reading anywhere from 300 to 400 degrees after driving at operating temp

 

[swathdiver]

I have a diablo tuner set on 87 econo tune and to disable the afm. 02s are tight, the cats are reading anywhere from 300 to 400 degrees after driving at operating temp

300-400 idling after a drive? That's quite cool in my experience.