So I searched and came up with only 2 threads with the mention of the PO421...honestly surprised!

What's interesting is that in both the threads both owners had an aftermarket header, so the reason for their CEL would be obvious (no 1st cat). But minus my Greddy EvoII canister, my exhaust system is stock.

Assuming bank #1 meant the first O2 sensor, does "below threshold" mean that the sensor isn't (all of a sudden) getting proper readings from the ecu? or proper readings from the exhaust gases (bad O2)?

I've not done anything to the car lately, and the CEL showed up while cruising down the road...nothing out of the ordinary. Guessing "Stewart" didn't like the fact the wife and I were test driving other cars today!

I had also read that a 2nd generation Eclipse O2 sensor is a direct match to ours? If I remember from the post, it was Alchemist that said that...so I can believe there's truth behind it. But has anyone ever used one?
*Edited for correction and quote : Thanks ahead of time for your help and assistance!

 

your cat is bad. the ECU look at the O2 sensor before and after the cat to determine the efficiency of the cat. if the 2 O2 sensors data is very close for certain amount of time, the ECU will kick on the check engine light. that why people that have aftermarket exhaust manifold will have the code cause i think the cat is part of the exhaust manifold. bank 1 mean the bank of cylinders where the number 1 cylinder is and 4 cylinders car only have one bank.

 

dam i just got this code yesterday too!!

 

Were you out test driving other cars too? LOL I think "Stewart" overheard us and decided to be nasty.

 

lol nope im only 18 (just turned) and still go to HS so i dont have the cash
but ill prob just fix it
if its the converter its only 130 for one on ebay (obx high flow,bolt on)
but i hope i fixed it by doing a couple things earlier

 

How many miles you got on your car? I change my second 02 at 80 000 miles... A O2 sensors worn out with the time and milage, I'll change the sensors before the cat. (That work good on my car...)

A good read about Oxygen sensors...

http://www.ngksparkplugs.com/tech_su...x.asp?mode=nml

 

I've got 85k miles, so I know an O2 replacement was coming up on the things-to-do list...but it's always at the most inconvenient times!

 

I bougth mine from this compagnie:

http://www.automedicsupply.com/

Good pprice and fast shipping. They work great too.

(Don't buy the universal one... They don't come with the plug.)

 

if you are using the stock header and you don't have a lot of cash i have my stock header with a working cat that i could send your way for a few bucks.

alternatively you can do the non-fouler trick on the 2nd O2 sensor for maybe five bucks and fifteen minutes of your time and that CEL will disappear.

 

If the second O2 sensors is dead, the trick of the non-fouler will not work.

At 85 000 miles, I'm sure the O2 sensors is dead. (Like I have on my car.... Everything was fine and one day, bang the cel for the P0421.)

 

So with it saying bank #1, doesn't that mean the first O2 sensor though?

 

i got my code cleared 2 days ago and it hasnt came back!!
i think it was because my spark plug wire was really loose!

 

How'd you clear it? Disconnect the battery?

 

nope when u take it to autozone they clear it if u ask them without resetting everything (stereo ,clock)
or you can also reset it by disconnecting the battery for 5 mins!

 

Well dang! The guy never asked while I was there...and it wasn't like they're busy either. I was their only customer! LOL I probably end up disconnecting the battery anyways...it has been a while and fuel has been dipping a little low lately.

Thx