Hey my intercooler piping fell off a couple weeks ago. This has happened before. The car would throw a code, then it would disappear... but not this time.

Now its throwing
P0420 Catalyst efficiency below threshold

I tried to reset this a few times and it keeps coming back.

I dont have a test pipe. Most of the time i see these codes on the forums its for a test pipe.

So is my cat bad, or one of my o2's?
thanks.

 

do you have a cel eliminator ? tried a antifouler thingy? i had a similar issue on my oz not a evo but related in the trouble code
http://www.obd-codes.com/p0420

on mine my precat is failing and the its integrated into the header....

does it always comback after a reset? or does it take awhile for itto reappear?
imthinkin if its always ther after u clear it then somthin maybe bad ie o2 sensors

 

Yeah but aren't the anti foulers mostly for guys with est pipes not people with the cats?

 

Ya foulers are most commonly used for those with no cat. I can't recall hearing of anyone using them with the stock cat.

Maybe the cat has failed, maybe the honeycomb inside has collapsed.

 

Even a hi-flow cat can cause a P0420. I cleared it about four times, but it kept coming back. I finally installed an anti-fouler adapter on the o2 sensor, cleared the code, and that fixed the problem. On my 2004 Evo, I had to use the 90 degree type because a straight fitting jammed the o2 wires into the body pan. Probably depends on the brand of exhaust you have.

 

I dont have a test pipe. The code will go away once i reset it... but if i get it on it immediately, the code comes back on. I dont know if its my cat or an 02, or how i can determine which it is.

 

i think be cheaper to get a cel eliminator to fix it and go about your way. or if like other guy said, if the comb inside the cat collapsed, then it would need be replaced. depending on what 02 sensor has failed up or downstream, the price varies $71.99 for the downstream & $84.99 for the upstream. those prices have a 3month warr accordign to the autozone website.
http://www.autozone.com/autozone/par...h?sortType=low

they have ones that have a 1yr warr on them but those cost more.

im in same boat as you, luckly i dont have to worry about it untill my smogg is due next april.. btw, how does the car drive? just curious if a bad cat causes a problem.

 

I have a high flow cat and had to get the anti-fouler fix.

 

so am i better off paying off someone to diagnose the problem to figure it out? how do i tell if its the cat or one of the 02's? i want to fix it so i can sell the car.