PO420 code keeps coming back only when 4WD is used

Hello all. Hoping someone can shed some light on this issue. I have a persistent PO420 code. I can't afford new cats right now, but just curious why the code only comes up when 4 wheel drive is used. I changed the O2 sensor with denso, cleaned the MAF, new air filter PCV valve and seafoamed. The code was off for 3k miles. Used the 4wd yesterday and boom. Comes back on. This has happened twice. Thanks in advance for any advice.

 

That code shouldn’t have anything to do with you using 4x4. Unless vibration are effecting a bad cat in some way.

 

Yeah, I know the 4wd system shouldn't have anything to do with it, but the CEL has been off for almost 3k miles and came back after using the 4wd. 2 months ago, the same thing happened. CEL was out for 2500 miles, used the 4wd and popped the cel. Maybe because the engine is working harder with the 4wd on. Thanks for the reply

 

Only real way would be to inspect your cats. Mine were plugged up and I didn't know. I needed new cats. I have been P0420 free for a while

 

Well, if you can't afford a cat and you want the light off, use an 18mm fouler on the 02 sensor after the cat. It will act as a spacer and your computer will be tricked into thinking the catalytic converter is working properly because the sensor will be higher above the exhaust stream and read less nox, CO's, HC's, c02, but more o2. If you're do for a smog, take it out right before you smog it so it passes the visual inspection. IDK how you do smogs where your from, but on an 01 we just plug it in a computer without taking emissions readings in California. Just keep your fingers crossed that the cat isn't plugged though.

 

Shouldn’t of seafoamed it....which O2 sensor did you change both?

 

No, just the downstream O2. I didn't touch the other sensor. Why shouldnt I have seafoamed?

 

Just picked up the non-fouler. Will definitely try that. In NY they just plug into the OBD port. Thanks for the info

 

Talked to a mechanic and he told me if the truck runs well, doesnt hesitate and runs smooth, the cats are probably fine. It may have to do with an exhaust leak near the manifold. I have a couple things to check I guess. Thanks for the advice

 

Change out both O2’s. I don’t know what the hell that seafoam stuff is so I wouldn’t use it. A lil crud in the intake is good. Yes a exhaust leak will mess up the O2 reading and it will lean out I think.

 

I only have one more emmisions test in a few months then I’m good forever and it’s getting antique tags in spring of 21.....