Had this code a couple months ago and went away after a day or so. Back on, just in time for inspection. I've been doing some recearch and seems to be quite a lot of these. 85,000 miles so out of emissions warranty. Is there an easy way to diagnose whether it is cat failure or oxygen sensor? Had the white smoke on start up tsb done about a year ago, wonder if that could have caused cat to fail. Starting to miss my 2000 7.3 that I traded for this truck.

 

Had CEL come on and was this code in my 16 3.5 Eco a couple years ago. Cleared it and it didn't come back on until a couple weeks ago. Noticed that both days were very wet with rain and snow. Ended up buying the up and downstream sensors for that side in the hopes to change them, but I've seen some folks mention to clean the MAF sensors first before digging into the catalytic converters.

I find that this code stays as a freeze frame, but won't trip the actual CEL unless we have a very wet day.

 

A code 420 and or 430 is very definitive to CAT failure.
The front and rear Ox Sensors are only telling you of the fact, not the cause.
The OX Sensors detect Oxygen.
The rear only looks for the required amount of Ox storage in the middle of the Cat.
The rear signal is compared to the front as the way it knows what the condition is.
When they go out of limits the code is set. [ cat is not cleaning the exhaust well enough ]
Cannot get around it.
Ox Sensors have their own fault codes.
Good luck.

 

Yep, I've seen your posts and believe you, thanks for the knowledge. I just need to find out why the cat failed before throwing good money after bad.

 

I had this very same issue with my 2015 3.5 Eco. Would get random catalytic converter efficiency codes that would turn the engine code light on. And the only thing that was constant was that it would be a rainy, wet day when it would illuminate the light. I could clear code and it might not come back on for months or weeks but then on a wet, rainy day it would come back on. I never did figure out entirely what was going on except that when I changed the cats I haven't had the light come back on. I know that doesn't help you much but it does help make the point that if you get a 420 or 430 code it more than likely means the actual cat is probably bad.