How to get rid of a P0421 CEL...?

[AutoXRacer]

How do you non-catted guys get away with not having cels?
I think I read some where that you can use a plug defouler or something like that...?

Thanks!! (2thumbs)

[speedi3]

The Cel for non-cats is p0139. Not sure what the p0421 is for. But you are correct get a non-fouler. Most autoparts store carry them. I still get a light every now and then I clear it and keep driving for 4-6 months and then it comes back.

[Shane5425]

Warm Up Catalyst Efficiency Below Threshold (Bank 1)
Symptoms

You will likely not notice any drivability problems, although there may be symptoms. The code may be more likely to occur after the engine has had numerous cold starts in the past 1-2 days.
Causes

A code P0421 may mean that one or more of the following has happened:

The catalytic converter is no longer functioning properly
An oxygen sensor is not reading (functioning) properly
A sparkplug is fouled up

[schumann1913]

yea ive been having the same code on my protege...i have a 3 in dp with a high flow and the code came out of nowehere...i changed the plugs and the ones i pulled out were fine...could it be that my high flow is bad? and is there a way to check your 02 sensors to see if they are working well?

[Shane5425]

do the defouler trick..

[wisniaPl]

I thought you have cpe catted downpipe

[AutoXRacer]

Did the non-fouler trick!! Worked like a charm!!!

I bought a long 18mm sparkplug non-fouler and bored out the ID to match the O2 sensor tip...

[ghettoracingkid]

Does the non fouler trick effect gasmileage at all

I got all stock stuff but i got the P0421 code and dont want to redo my exhuast with 189000

[bazooka joe]

Does the non fouler trick effect gasmileage at all

I got all stock stuff but i got the P0421 code and dont want to redo my exhuast with 189000
nope

[AutoXRacer]

No, the second (rear) O2 is there to only verify the catalytic converter is working...

[Shane5425]

correct, the first o2 is reading what is comming from the engine, the 2nd one is behind the cat and is reading what the air should read when it leaves the cat..

[Flspeed]

Ok, Im a newby to the mazda world and dont really know what a defouler is. Can some one drop me a hint?

[dirtyd]

AutoX - Did you use basically the same steps as shown in this thread?

http://www.mazdas247.com/forum/showthread.php?t=123634664

I keep throwing a CEL now that I have my DP and MP installed and its starting to piss me off! Did you only do it to the second o2 sensor?

Thanks for the help!

[AutoXRacer]

AutoX - Did you use basically the same steps as shown in this thread?

http://www.mazdas247.com/forum/showthread.php?t=123634664

I keep throwing a CEL now that I have my DP and MP installed and its starting to piss me off! Did you only do it to the second o2 sensor?

Thanks for the help!

Yep thats pretty much it... Bought a 18mm long defouler, bored/drilled out the inside, screwed in the O2, and bolted it back up to the DP...

You only do this to the rear (2nd) O2!!!!

[wisniaPl]

why you did this having catted dp??

[AutoXRacer]

My cat failed...my exhaust temps are at 1500* and the cat was only able to handle 1300*. I am getting it replaced under warranty. There is a new cat now that is able to handle the MS3 exhaust temps without any issues.

[wisniaPl]

so new cpe prducts shouldnt have problem with cat failing??

[dirtyd]

Yeah...I dont have any cats...I guess I'll just try that non-fouler on the second o2 and see where that gets me.

[ghettoracingkid]

how do you test the 2nd O2 sensor.

I think im having problem with my cat but I dont want to drop that kidna change if its not.

[AutoXRacer]

You don't test it...you get a CEL that say the Cat is below its efficiency range...then you know your Cat is toast...

[ghettoracingkid]

I forgot where the post is but someone said you can test the downstream O2.

I guess ill ave to suck it up since I changed the O2's not to long ago

[clos561]

isnt that too lean at idle cel?

[ericrapp]

how do you test the 2nd O2 sensor.

I think im having problem with my cat but I dont want to drop that kidna change if its not. Take your car to a local auto parts store and have them read your codes, usually for free. really easy. then you could ask mazda or us whether you need to spend money on the sensor. Occassionally i hear the rear o2 will dirty up with rich conditions and not read well. And Mazda can run a resistance check on it. You will code if it fails, the ecu will detect it. I hope you can check out the codes to see what is up with exhaust. Mods can effect your ecu too as you probably know, but check em out for sure and good luck!