P0420 code issues

Shane Collins · March 13

I’m getting the P0420 code randomly. I reset it and sometimes it takes a couple days to come back, other times it’s a few minutes. I recently installed a Range Technology AFM/DFM disabled which completely stopped the engine code from coming back. I was curious this morning and unplugged the disabler to see if the code would come back and it did within an hour of my commute. This makes me think it’s not the catalytic converter but possible an issue when the truck switches down to 4 cylinders. Anyone come across this issue and know of a fix? Thanks!

CamGTP · March 13

If the 2 cylinders on the drivers side that shut down with AFM are burning oil or something along those lines, I could see that tripping a cat code because it's polluting the exhaust on that side. That's just a wild guess.

I'd just keep the AFM off and not worry anymore lol

newdude · March 13

10 hours ago, Shane Collins said:

I’m getting the P0420 code randomly. I reset it and sometimes it takes a couple days to come back, other times it’s a few minutes. I recently installed a Range Technology AFM/DFM disabled which completely stopped the engine code from coming back. I was curious this morning and unplugged the disabler to see if the code would come back and it did within an hour of my commute. This makes me think it’s not the catalytic converter but possible an issue when the truck switches down to 4 cylinders. Anyone come across this issue and know of a fix? Thanks!

No. Its because the Range interrupts the ECMs ability to properly run the diagnostic monitors on board. If the monitors don't run, it can't run the self tests of the 30 or so DTCs it checks for proper engine funciton, P0420 being one of them.

So the Range is just masking the issue. The P0420 is there for a reason and needs to be diagnosed. Could be a failed converter, bad O2 senors, exhaust leak, etc.

Edited March 13 by newdude