Cel Code P0421

BlkMica_03

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Mazda, Protege 5
hey guys my check engine light come on the other day so i stopped at advanced and had the run it and i get code P0421 which is "The PCM has determined that the warm up catalyst efficiency for bank 1 is below threshold for the current engine operating conitions"

any ideas what this is and how to correct it???

thanks in advance guys
 
P0421 is a catalytic converter effeciency below threshold problem I believe (you need to replace the catalytic converter)

minnimum emissions warranty is standard 8years/80,000miles in the united states (this is for any car, and not manufacture specific) just take it to a dealership and get them to verify the problem and they'll replace it. You should only have to pay for labor.
 
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Could that CEL be oxygen sensor-related since the oxygen sensors are used to determine if the cats are working or not?
 
Kansei said:
Could that CEL be oxygen sensor-related since the oxygen sensors are used to determine if the cats are working or not?
it could, there's only one O2 sensor past the cat that detects if the cat is working correctly. Usualy if an O2 sensor isn't working correctly though it gives a seperate code for that, usualy something like P1138 (HO2S Bank 1 Sensor 2 Signal Above 0.45v (A/F Ratio Too Rich)). the O2 sensor should be under the emissions warranty too I believe, but I think it's just the cat, in either case, to the dealership we go!
 
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well being that i have the wagner shorty header im pretty much screwed the dealer wont fix it :-(
 
should i still have to do the non fouler even thought the shorty is supossed to be emissions legal ?
 
i just had the same code ran on my speed, I put the vibrant on and i think the jackass who installed it put the 2nd o2 sensor in front of the Cat. If i relocate that o2 sensor behind the Cat will that remedy the code? Sorry for a thread jack.
 
210_ZOOM said:
i just had the same code ran on my speed, I put the vibrant on and i think the jackass who installed it put the 2nd o2 sensor in front of the Cat. If i relocate that o2 sensor behind the Cat will that remedy the code? Sorry for a thread jack.
The sensors are the same, so it wouldn't matter which you put where, however the two sensors have very different cable legnths, the one closest to the EGR pipe has about 1/2 the cable legnth of the one past the cat, if he damaged or lost the one that's closest to the EGR pipe, it'll be pretty noticable that there's *alot* of slack in the cable for the one that's installed closest to the EGR pipe, which of course would set off the code since there's no sensor to read off of . Now, if he just forgot to plug in one of the sensors to the plugs just below the EGR pipe thats different. If you look at the picture I attached, the first red circle shows where the two plugs are for the O2 sensors, and the second red circle is the plug for the O2 sensor in front of the cat(that is the cause of the code)

although, I don't know why on earth you would need to take off the exhaust manifold & O2 sensor for a vibrant cat-back. (poke)
 

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sephiroth said:
The sensors are the same, so it wouldn't matter which you put where, however the two sensors have very different cable legnths, the one closest to the EGR pipe has about 1/2 the cable legnth of the one past the cat, if he damaged or lost the one that's closest to the EGR pipe, it'll be pretty noticable that there's *alot* of slack in the cable for the one that's installed closest to the EGR pipe, which of course would set off the code since there's no sensor to read off of . Now, if he just forgot to plug in one of the sensors to the plugs just below the EGR pipe thats different. If you look at the picture I attached, the first red circle shows where the two plugs are for the O2 sensors, and the second red circle is the plug for the O2 sensor in front of the cat(that is the cause of the code)

although, I don't know why on earth you would need to take off the exhaust manifold & O2 sensor for a vibrant cat-back. (poke)

Thanks for your reply, i have an MSP so, the vibrant bolts up to the Jpipe on the turbo. The first sensor should not have been effected at all by this.It also removes one cat (if my memory serves me correctly) The second O2 sensor though should be installed behind the cat (i believe) That is what i believe to be throwing the code. Any further informations on this will be greatly appreciated. If my assumptions are correct or not im not 100% sure. Thanks again
 
210_ZOOM, once you remove 1 cat, you'll throw a CEL. you need to use an MIL eliminator, or even better, use the non-fouler method
 
you *could* put the damn stock exhaust manifold back on, drive to the dealer and get a new cat for FREE and then put your 'shorty header' back on you know
 
smo0f said:
210_ZOOM, once you remove 1 cat, you'll throw a CEL. you need to use an MIL eliminator, or even better, use the non-fouler method

any instructions on that?
 
i dont have the stocker if i got a differnt header and did the non fouler would this fix the problem???

also will it hurt the car to run with the code (ex. limp mode)
or anything?
 
yea there's a how-to for the non spark plug fouler method (not the link you posted)
 
so will an obx or ?? header and the non fouler method fix the problem im having. and will there be any damage to the car until this is fixed?
 
I have this code. Last night I removed the catalytic converter and discovered that the dual layer metal gasket that is between the ex manifold and cat is broken. It is actually broken through both metal sheets in 2 places and is starting to crack apart in a 3rd place.

There was a post somewhere here that showed a MAZDA troubleshooting sheet for this error code. I believe the 3 suspect causes were
Oxygen Sensor
Catalytic Converter
Exhaust leak.

MY QUESTION TO THE FORUM IS
Should I just replace the gasket hoping it is an exhaust leak and see if the code goes out? Or go ahead and replace the whole cat as well and get it done with?

I do not want to use the CEL eliminator for many reasons.

When I shake the cat it doesn't rattle or anything, but could be "poisoned"

I don't see exhaust carbon on the manifold shield or anything else suggesting a leak (would I if there was???)

FYI
Cat with installation from the dealer $1200+

New Cat from Dealer parts store $358 with inlet and outlet gaskets plus bolts.

New cat from www.convertergeek.com is $225 after core is returned.

INlet gasket at the dealer is $28.09

Outlet gasket at the dearler is $13.06

I have had this code for over 2 years now and no problems that I know of and gas mileage is 33mpg highway documented. Unfortunately, I moved to Raleigh, NC which has emissions inspections and now I have to fix the CEL.

Thank you,
Chris
 

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