Code P0420

[carlover]

Ive been battling this code for over a year now. Ive replaced both o2 sensors and the converter. no matter what it seems to just keep coming back. ive done a search and it seems no one has come up with a concrete answer or solution for this code. ive read about the o2 eliminators but how will that affect the smog test i have to do for my registration?? Any help would be greatly appreciated.

 

[MountaineerGreen]

I get a similar code occasionally, something about "catylist (sp?) below efficiency threshold". I clear the code and it just comes back every once in a while.

You could trick your computer into thinking the O2 sensors were there, and if they don't look under your truck extensively, you may be able to get by with it. That is, assuming your truck is running OK. But then again CA is strict about that kind of thing.

 

[carlover]

i clear the code and it comes back within 10 miles of driving. It does run pretty rough and i thought that was the "tune" the computer was adjusting to because of the code. All major tuneup things have been done in the last two months. I have to pass smog this month...

 

[MountaineerGreen]

You have a custom tune?

 

[schmoken]

FWIW, I was told the 0420 code comes from the sensor downstream of the cat. It's more of an indication of the cat's condition, with no effect on engine tuning.

 

[MountaineerGreen]

Right, but if a custom tune is causing a rich condition, the cat may not be able to burn everything off.

Did you remove your secondary cats?

 

[carlover]

No custom tune. I wasa referring to the fact that most pcm's self adjust tunes for certain conditions. Like if the o2's dont send the proper signal they pcm will adjust for more fuel or less depending on the reading. I know if o2 sensors are bad it will cause the pcm to stay in open loop because it never "see's" the correct readings. I have the ohv v6 so i only have the one dual cat setup and it was replaced along with both 02 sensors very recently.