Hey guys I recently diagnosed my CEL and the code I got was a P0421: "Warm Up Catalyst Efficiency Below Threshold (Bank1)."

My question is what do I need to do to fix this problem?

 

Catalytic converter, possibly an o2 sensor.

I say clear the code, and see if it comes back.

 

i tried that earlier today its still there...my friend told me it might be my headers, but im not sure how my headers would affect my cat warming up to its threshold?

 

Thats just a stupid name for it. Trust me. Oh.. and your car has one header

Well, are you sure you cleared it right? It should go off for how ever short a perior of time... and if it didnt then you didnt do it right.

 

yea....it went off then like 30min later it came back on with the same code. . . yea i have only ONE header lol

 

Replace the converter, thats your problem.

 

.....what year ?

how many miles ?

one or two cats ?

how long / miles have you had the header on ?

 

2003 Lancer ES...about 93k, and it has 1 cat, also the header on it is stock. So I know for at least 30k miles i've had the headers.

 

first , replace the O2 sensor or sensors. muich easier than replacing the cat.

if that does not do it, replace the cat.

you will not be "wasting money" doing the sensor(s) if you end up having to replace the cat because if you need to replace a cat the O2 sensore should be done at the same time anyway..

 

why dont i see the final outcome? How did you guys fix this problem finally?
who knows, thank a hundred.