Hey Quinny,
p0421 is a catalytic converter efficiency code and since you have already replaced the 2 post cat O2's then it sounds like you have a cat that has failed. Which bank is it?

Chris

Answered by carundell
18 questions asked

PO421 is bank 1. How many cats are there on this thing two or three?
I wonder how long I have til it goes bad on me.

Response from quinny24
1 question asked

what is the difference between this code and PO420?
PO421 says "warmup catalyst efficiency below threshold (bank 1)" and
PO420 says"catalyst system efficiency below threshold (bank 1)"?????

Response from quinny24
1 question asked

Just for everyones info. I ended up taking my Montero Sport to Meineke and was told I needed a new cat., the owner of Meineke told me a direct fit would be $900 plus but that he could find one for much less than that probably even half. well after searching for 2 days he calls and tells me he can't get an aftermarket direct fit and I need to get it from the dealer for the original estimate of $900 plus.
I am starting to get very bitter at this thing, for one thing I bought a car with California emissions (who ever checks for that when they go out to buy a car in Pennsylvania). Well at 44 I'm still living and learning LOL

Response from quinny24
1 question asked