P0421 Code won't go away!

[paultt]

I have a 2005 mazda 3 sport GT and have had a P0421 engine code since 62000km!

OBII Definition is :Warm Up Catalyst Efficiency Below Threshold (Bank 1)

I have replaced both upstream and down stream O2 sensors (only has the 2 not Cali model) as well as coils, and spark plugs. I also tested the exhaust pipe directly before and after the CAT with a temperature gun to check for clogging and two readings were within 2-3 degrees of one another. I do not know what to check next and do not want to get into an 800 manifold as it is hard to believe that the CAT would fail at 62k KM!
Hopefully I am overlooking something basic.

Also, when I clear the code and continue to drive it takes over 500km of driving to come back and doesn't need to have start and stops to activate (often clear and continue driving and it comes back on). Once the light comes on the car also acts up and does not idle steadily at a stand still. When the code is cleared this problem also goes away and the car idles like a dream.

Any help/input is greatly appreciated so thank you in advance!

[Kiyomi]

the reason why the car does not idle or run right with the engine light on is because it is giving the engine more fuel that needed or possibly a little bit of misfire because the ecu is sensing something is wrong. put in safe mode. not really hurting the engine, just wont run as good. bring it in either to a dealer or aph if you cant find the fix. gl o, and wut mods you got done to the car, or is it stock?

[MPS]

you need a new cat

[TheMAN]

why are you wasting money on new sensors when the code is telling you exactly what is wrong with the car?
when you get a cat failure code, it is 99% always true and you should believe it instead of wasting money on sensors... if the sensors were bad, it would've told you so!

and using a temperature gun to check the cat is not definitive... the ONLY way to check a cat is either with an exhaust gas analyser or using the scan tool to monitor both front and rear O2 sensor readings
again, you wasted your time by not knowing proper diagnostic methods

with only 62k, your car is still under the emissions warranty... had you read your manual in the first place, you would've known this and not waste time/money!
so take it in to the dealer and get them to replace the cats under WARRANTY!

[WingZero_]

+1 on the cat being the problem.

the reason why the car does not idle or run right with the engine light on is because it is giving the engine more fuel that needed or possibly a little bit of misfire because the ecu is sensing something is wrong. put in safe mode. not really hurting the engine, just wont run as good. bring it in either to a dealer or aph if you cant find the fix. gl o, and wut mods you got done to the car, or is it stock?

Wrong P0421 does not cause any type of driving/idling problems. Any car that has a header and no fix has this CEL. A secondary O2 sensor merely tells when your cat is acting up, or in a header case, not there.

[MPS]

here this persons is giving away 2 of them for free
since you can't read codes make you can used the free cat

http://toronto.kijiji.ca/c-pets-cats...AdIdZ311740492

[bluemazda3]

lol @ vlad... hahaha

[TheMAN]

+1 on the cat being the problem.



Wrong P0421 does not cause any type of driving/idling problems. Any car that has a header and no fix has this CEL. A secondary O2 sensor merely tells when your cat is acting up, or in a header case, not there.

but, a clogged cat COULD cause driveability problems

[TheMAN]

here this persons is giving away 2 of them for free
since you can't read codes make you can used the free cat

http://toronto.kijiji.ca/c-pets-cats...AdIdZ311740492

meow, what's the problem here?

[WingZero_]

but, a clogged cat COULD cause driveability problems

Hence the +1 on the cat being the problem.

[Kiyomi]

+1 on the cat being the problem.



Wrong P0421 does not cause any type of driving/idling problems. Any car that has a header and no fix has this CEL. A secondary O2 sensor merely tells when your cat is acting up, or in a header case, not there.

Are you still going on about the header... I was just trying to help, if all you do is chirp people, why are you on the forum? suggest a solution.

[TheMAN]

Hence the +1 on the cat being the problem.

oops, didn't notice

thanks for the +1 though

[Donshaw]

+1
I believe it is the CAT too but there are better ways of proving your point then to insult other people.

Are you still going on about the header... I was just trying to help, if all you do is chirp people, why are you on the forum? suggest a solution.

[WingZero_]

Are you still going on about the header... I was just trying to help, if all you do is chirp people, why are you on the forum? suggest a solution.

Just don't like people giving newbs misinformation.

[paultt]

here this persons is giving away 2 of them for free
since you can't read codes make you can used the free cat

http://toronto.kijiji.ca/c-pets-cats...AdIdZ311740492

Real professional response.

Thank you however to some others with actual input.

Also, replacing O2 sensors was not a was of time because by that point there were 80k km on the car and they are known to require replacement by this service interval, so seeing as they would require replacement in the near future anyways it was worth a shot (and since I order all my parts from the states for the most part for less than half what they cost here) the cost was very minimal.

My waste of time was joining this forum and being told what I already suspected when hoping for actual input, as engine codes are not always definite and can sometimes involve a simple fix.

and MPS I don't want to buy the kittens you have been sitting around making all day. Enjoy.

[timezwasting]

apologies on reviving an old thread, but I am still new and can't create a new thread. I have the the exact same car, 2005 Mazda3 GT, same DCT P0421 but I'm @ 114,000km.

I had a local mechanic recommed the O2 sensors, but before I invest any money in fixing this issue, should I just opt for the $700+ catalitic converter.

Can anyone recommend OEM or aftermarket for the catalitic converter?

I have everything stock on my car.