CPE CAT failure - CEL code P0421

steefnap

Member
So after about a year of driving with the CPE DP and Catback exhaust (single pipe), I started throwing CEL's for no reason. It would come up for a few hours, then go away. A few days later, it would come back. It has been intermittent now for a few months.

I took it into my dealer to get the CEL checked out, and they gave back the code of P0421 which means that the catalytic converter is not working. They gave me a printout of their diagnostic software, and showed me the O2S12 line as compared to LONGFT1, O2S11, and SHRTFT1 (don't ask me what they are, I don't know... I am assuming oxygen sensors?). The latter three lines are fairly straight and consistent throughout the reading.

The O2S12 line looks like an siesmic graph during an earthquake, where the pen goes all wacky and draws squiggly lines during the tremors. They said that the line should be even, in line the rest of them. Because of this, my cat is not working and the emissions are not clean. I can tell just by my nose as well, that it is rather pungent compared to before. Also, my single outlet at the back of the car is caked with soot and whatnot, so it can't be burning very clean at all.

Two questions, and the first one is for CPE:

1. What sort of CPE Warranty is there on these items?

2. If no warranty, can just the cat be changed out, or does it have to be the whole DP? If I can't just change the cat, I may just go back to the stock DP...

If anyone wants to see the graph readout, I can scan it at work tomorrow and post the image.
 
Call cp-e or visit their website to find out the warranty.

The cat could be changed, bring it to a muffler shop with a new high flow cat and have them cut the old one out and put a new one.

I would personally get a spark plug/o2 spacer and install it to the o2 sensor that is throwing the code to trick it.
 
So after about a year of driving with the CPE DP and Catback exhaust (single pipe), I started throwing CEL's for no reason. It would come up for a few hours, then go away. A few days later, it would come back. It has been intermittent now for a few months.

I took it into my dealer to get the CEL checked out, and they gave back the code of P0421 which means that the catalytic converter is not working. They gave me a printout of their diagnostic software, and showed me the O2S12 line as compared to LONGFT1, O2S11, and SHRTFT1 (don't ask me what they are, I don't know... I am assuming oxygen sensors?). The latter three lines are fairly straight and consistent throughout the reading.

The O2S12 line looks like an siesmic graph during an earthquake, where the pen goes all wacky and draws squiggly lines during the tremors. They said that the line should be even, in line the rest of them. Because of this, my cat is not working and the emissions are not clean. I can tell just by my nose as well, that it is rather pungent compared to before. Also, my single outlet at the back of the car is caked with soot and whatnot, so it can't be burning very clean at all.

Two questions, and the first one is for CPE:

1. What sort of CPE Warranty is there on these items?

2. If no warranty, can just the cat be changed out, or does it have to be the whole DP? If I can't just change the cat, I may just go back to the stock DP...

If anyone wants to see the graph readout, I can scan it at work tomorrow and post the image.

Sounds like the rear O2 sensor is contaminated with fuel/oil/carbon. I would clean it/replace it and try again before looking at the cat itself...
 
Silly question... as I have not been under my car that much other than to change the oil and do the Engine mount upgrade... but where is the O2 sensor? Is it easily accessible/replaceable/cleanable? I've searched the forums and can't find a quick answer.
 
Silly question... as I have not been under my car that much other than to change the oil and do the Engine mount upgrade... but where is the O2 sensor? Is it easily accessible/replaceable/cleanable? I've searched the forums and can't find a quick answer.

Yeah, the rear O2 is in the downpipe after the first cat. You can get to it easily from under the car. The connector though, is a bit more effort. It is mounted in a bracket under the turbo inlet pipe accessable from under the hood... The "other" mazda forum is much more active than this one for information threads.
 
what would be the best way to clean an O2 sensor? Any typical cleaning agents I should be aware of that do a good job?
 
what would be the best way to clean an O2 sensor? Any typical cleaning agents I should be aware of that do a good job?


Any carb/contact/brake cleaner will work. Just douch it real good and blow it dry a few times. If this doesn't clear up the CEL, then cat OR O2 sensor is truly TU. I would suspect eht O2 first. They are ~$40 for Bosch at Advance, AutoZone, etc.
 
thanks for the feedback, Captain P5 and Forzda... now it's just a matter of making some calls and getting a little dirty! I will let you know how she goes...
 
waranty on mazda emissions is 8yrs or 80k miles. If you have a p0421 Catalyst Efficiency code it means your cat is not doing its job. The readings they gave you are probably either Short term fuel trims and long term fuel trims or o2 sensor voltage. High voltage rich, low voltage lean. O2 upstream shoudl swing up and down and downstream O2 should stay steady meaning the cat is buring any unused/unburnt fuel. If it looks like the upstream your cat is junk. Buy a new one or take it to the dealer for waranty. PM me or email me and i can look up your waranty info, I am a Mazda Master Technician.
 
hey mazda buddy let me ask you a couple of question i have an 06 speed6 with 45000 miles i have cpe intake hks blow valve test pipe and magnaflow exhaust. when the car was with like 10000 miles i had the i got the test pipe and i got the smoke issue ones at iddle and that was it . now the other night getting from work i left the car running for a few minutes and strted to smoke then it has not done it ever since. now am at close to off warranty and if i take it to the dealer it might not do it and what are my chances that they can take care of it if when the car it's at the dealer it does not smoke
 
waranty on mazda emissions is 8yrs or 80k miles. If you have a p0421 Catalyst Efficiency code it means your cat is not doing its job. The readings they gave you are probably either Short term fuel trims and long term fuel trims or o2 sensor voltage. High voltage rich, low voltage lean. O2 upstream shoudl swing up and down and downstream O2 should stay steady meaning the cat is buring any unused/unburnt fuel. If it looks like the upstream your cat is junk. Buy a new one or take it to the dealer for waranty. PM me or email me and i can look up your waranty info, I am a Mazda Master Technician.


TRXSandRacer02, did you read the original post where it says the OP has a Custom Performance Engineering (CPE) downpipe with a high flow cat in it? I don't think Mazda will warranty the little aftermarket cat...
 
the oiling issue is still being looked at from Mazda corporate to determine to extend the powertrain waranty of speed6's due to the excessive smoke at take off and at idle when cold. It is from oil at the turbo we believe but also pcm recalibrations for cold starting have corrected this also. If you are in waranty take it to the dealer and explain to them the situation or send me a pm with your vin and i can check your waranty info.
 
the oiling issue is still being looked at from Mazda corporate to determine to extend the powertrain waranty of speed6's due to the excessive smoke at take off and at idle when cold. It is from oil at the turbo we believe but also pcm recalibrations for cold starting have corrected this also. If you are in waranty take it to the dealer and explain to them the situation or send me a pm with your vin and i can check your waranty info.

I haven't heard of a smoking at take off and/or cold idle smoking problem. The (oil, not vapor or rich fuel) smoking problem occurs at hot and/or extended idle and actually clears up upon "take off". Is "Mazda corporate" truely looking at the correct problem, or are you just mistaken in your wording? I'm not a "Mazda Master Technician", but I do have a few certifications of my own. I also own several Mazdas... I do know a top Mazda Master Technician in this region (he just won a vacation trip from Mazda "corporate") but he doesn't monitor these forums. BTW, I wouldn't send you my VIN for any reason... What dealer do you work for?

Never mind, found it in your profile... Also, thanks for taking the time to post your experience. If you want to gain more info, check out the smoking turbo threads posted in the other Mazda forum, mazda 6 club dot com.
 
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Any updates?

Sorry guys, no updates as of yet. The last month has been a little busy for me. I got married and went oin my honeymoon, so that took a fair amount of my time! (butthump)

However, the odometer says that it's about time for an oil change, so I will be taking a look at the O2 sensor when I get under the car to do the change. I'll let you all know how I make out.
 
Well, I did the oil change yesterday. Once I had the car jacked up, I went back to the O2 sensor at the bottom of the downpipe and started unscrewing it. It twisted the attached wires somewhat, but not violently enough that I considered having to undo the other end (thank God)!

Once it popped out, I got a good look at it. It looked like it had been in someone's fireplace for about 3 years. Totally covered in black soot. I used some brake cleaner on it, wiped it down with a rag, used more brake cleaner, and let it drip-dry while I did the oil change.

Once the oil change was done, I went back to do the O2 sensor. Before putting the sensor back in, I pre-twisted the wires a bit so that it would be more or less untwisted after I had screwed it into place. I would say I probably twisted it 4 x 360 degrees before putting it back. Seemed to be fairly straight once it was snug in the DP.

Undid the negative battery terminal and pumped the brakes a few times to bleed the system of any residual electrical charge, to reset the ECU. As expected, no Check Engine light showed up after I started the engine up. I didn't hold my breathe though, because over the last 4-5 months, the CEL has come on and off several times on its own with the same code, so it comes and goes.

That being said, I did 250KM's yesterday, and didn't see so much as a flicker of CEL. So at least the computer agrees that the sensor is working properly at the moment. We will see what happens a couple months down the road. I suspect that the dual Mazda cats do a better job of burning off the stuff from the engine than the single upstream cat one, so perhaps I will have to do this every second or third oil change, just to maintain the sensor.

Time will tell, I suppose.
 
Well, I did the oil change yesterday. Once I had the car jacked up, I went back to the O2 sensor at the bottom of the downpipe and started unscrewing it. It twisted the attached wires somewhat, but not violently enough that I considered having to undo the other end (thank God)!

Once it popped out, I got a good look at it. It looked like it had been in someone's fireplace for about 3 years. Totally covered in black soot. I used some brake cleaner on it, wiped it down with a rag, used more brake cleaner, and let it drip-dry while I did the oil change.

Once the oil change was done, I went back to do the O2 sensor. Before putting the sensor back in, I pre-twisted the wires a bit so that it would be more or less untwisted after I had screwed it into place. I would say I probably twisted it 4 x 360 degrees before putting it back. Seemed to be fairly straight once it was snug in the DP.

Undid the negative battery terminal and pumped the brakes a few times to bleed the system of any residual electrical charge, to reset the ECU. As expected, no Check Engine light showed up after I started the engine up. I didn't hold my breathe though, because over the last 4-5 months, the CEL has come on and off several times on its own with the same code, so it comes and goes.

That being said, I did 250KM's yesterday, and didn't see so much as a flicker of CEL. So at least the computer agrees that the sensor is working properly at the moment. We will see what happens a couple months down the road. I suspect that the dual Mazda cats do a better job of burning off the stuff from the engine than the single upstream cat one, so perhaps I will have to do this every second or third oil change, just to maintain the sensor.

Time will tell, I suppose.


Hey, thanks for the update. Maybe it will work well for a while now...
 
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