P0430 still after 2 new catalytic converters

Randy O'Quinn · November 18, 2020

So, I have a 2014 Sierra 5.3 and I've had the P0430 bank 2 issue. I replaced the stock cat with the Walker aftermarket one and after 3 months the code came back up. I was able to have the Walker cat warrantied and got a Magnaflow one this time instead... Thinking it may have been the Walker cats. After breaking in the Walker cats I have the code popping back up along with other codes as well. I have changed the spark plugs, checked the oil and coolant for possible contamination, checked for exhaust leaks, ect. I'm about at my wits end and I'm hoping someone has some info that could possibly help me. I have enclosed screen shots of the codes that came up on my scan tool.

CamGTP · November 18, 2020

You could swap the rear o2 sensors side to side to see if the issues follows.

If it does not then I would space the o2 sensor out of the exhaust stream so it doesn't see as much exhaust gases passing by it. It's a pretty common trick to try and fool the sensor.

Randy O'Quinn · November 19, 2020

Yeah.... I wanna fix the problem tho. Both sensors are new and it did it with the old ones. I know I can get the spacers but I have emissions every 2 years and I don't want to fail.

SILVER SLED · November 19, 2020

Probably the converter again. I don't see much luck with aftermarket cat converters.

Randy O'Quinn · November 20, 2020

Your saying probably the converter again but what about the other codes? The U codes coming up in the ECM, BCM, ect. They are all communication codes. Can a insufficient catalyst reading cause communication issues between the modules and the catalytic converter?

SILVER SLED · November 20, 2020

10 hours ago, Randy O'Quinn said:

Your saying probably the converter again but what about the other codes? The U codes coming up in the ECM, BCM, ect. They are all communication codes. Can a insufficient catalyst reading cause communication issues between the modules and the catalytic converter?

Those other codes probably won't set a light. However the code for the catalytic converter not cleaning the exhaust like it's supposed to will definitely set a light.

How many miles are on your truck?

Edited November 21, 2020 by SILVER SLED

Randy O'Quinn · November 21, 2020

Just over 100k miles. I changed the plugs, keep up on my oil changes, all the o2 sensors have been replaced and are reading good on heated catalyst test. Just had the fluids changed at 80k miles as well.

Allterrxin · December 28, 2020

Did you ever figure out your issue? I had the same thing happened to me. Replaced both cats and the check engine light came back on. Have you tried to graph the codes O2 data and see what it tells you?

Vertical · January 29, 2021

I have the same problem. P0420 & P0430. Replaced the cats... No love. I was looking at the short term fuel trim and noticed a spike in added fuel with my foot off the throttle while coasting to a stop. I thought that was weird. My rear O2 sensors are super flat most of the time - meaning my cats are working well. my front O2 are bouncing heavily - like they should. So it all looks great. Dealer says cats are bad replace & relearn $1750.

My scan tool & sensors say otherwise. Im thinking that gm programed some sort of fail safe if you use aftermarket cats that throws a code to push a P0420 & P0430 code. As evidence I will upload a relearn procedure that my service manager printed out for me