I have a 2014 Silverado 1500 5.3 with 230,000 miles. Recently I got a P0420 and P0430 catalyst system efficiency below threshold Bank 1 & 2. So I replaced the Y pipe with the catalytic converters as well as both upstream and downstream sensors, cleared the codes and the light came right back on after 50 miles of driving. So I then looked for exhaust leaks and found my manifold was leaking, so I replaced both manifold gaskets as well as the seals on the Y pipe and confirmed no more exhaust leak. Still the light came back. So then I replaced my MAF sensor and all 8 fuel injectors because I had run out of ideas. Still the light returned. I’ve also confirmed with my scanner that the O2 sensors are reading somewhere around .75-.85 volts which is within the threshold of where it should be. So now I’ve read some forums of people going to the dealer and reflashing their ECU to fix this issue. Will this work? Just curious if anyone else here has any experience with this or any advice, I’ve just run out of ideas. Thank you

 

if there is a tsb for a flash...get it done.

did you put on good quality cats? cheap cats will cause the codes to reset.

the ecm compares the switching rates of the front 02 vs the rear 02 sensors. if they switch at the same rate the dtc sets.
the 02 should switch from 0.1 to 0.9volts...graph the data and watch the switch rate.

if you have old front 02 sensors and new rear 02 it can set the dtc.

 

There’s no recall that I know of, I was just curious if a reflash of my ECU would help my issue. As far as the switch rate that’s something I’m not familiar with. I would have to further research that and graph it on my scanner to see. I thought as long as the voltage was under 1.0 it would pass, which they do. But both upstream and downstream sensors were replaced at the same time.

 

Make sure there are no exhaust leaks. Have seen leak at the clamp at the rear of the converter pipe causing cat codes. Can Google PIP3119P for a GM document on Converter break in procedure.

 

As tech2 stated O2 sensors 1 should vary between .1 and .9v, and O2 sensors 2 should be relatively flat around .7v. If sensors 2 vary like sensors 1 then the code will set as the cats are not doing the job. Hope this helps.

 

tsb is not a recall. its a tech bulletin from the manufacturer that suggests fixes for problems. Module updates would only help if they address your concern in the flash. Only way to know is to have someone with access to gm programming updates and they can read what the updated program is programmed to fix. Or read thru TSB to see if a flash has been done to address this.
if no flash is available, all 02 are new and no 02 codes are setting...and the switch rates are the same front to back...the replacement cats are the problem. cheap cats have low cerium content...the element that stores oxygen in he cat. post a link to what cats you bought