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icecats87
07-22-2010, 06:45 PM
Engine light came on today so read the code and it was PO420, looked it up and said something about maybe a bad cat, but i just put a high flow cat on not even 2 weeks ago, so i was wondering what else could be wrong, i got the cat from mpracing

remiljr
07-23-2010, 12:07 AM
high flow.......gamble for 02 code.... ur the unlucky one... check sensor connections and if all are working and tight.... high flow cat throwng 02 code.

westerndragon
07-23-2010, 05:46 AM
P0420 take the jibbahs out of your exhaust pipe

[ChaosweaveR]
07-23-2010, 07:53 AM
Change the cat, it's bad.

AaronGTR
07-23-2010, 03:10 PM
P0420 is for catalyst system low efficiency. Very common to get this code when adding a high flow cat. It has to do with the rear o2 sensor. The cars computer checks to see how well the cat is working but checking how fast the rear O2 sensor reacts to changes in the AFR that the front O2 sees. Basically if the cat is working efficiently it will burn up most of the stuff and the reading from the rear O2 will change very slowly compared to the front O2.

Of course when you add a high flow cat it typically has a smaller core with larger holes for less flow resistance, but therefore it normally is not as efficient at burning up emissions so some will pass through and the rear O2 will see that and set a code.

Possible fixes for this... A) get a slightly larger high flow cat that will have a longer core which will give it more time to burn the exhaust gases before hitting the rear O2, B) put some heat wrap around your downpipe to try and hold heat in and help the cat light off faster and burn more efficiently, or C) don't worry about it and ditch the rear O2 sensor. If you chose option C you'll need either a rear O2 simulator or a tuned PCM with the rear O2 codes deactivated. ;)

icecats87
07-23-2010, 04:00 PM
P0420 is for catalyst system low efficiency. Very common to get this code when adding a high flow cat. It has to do with the rear o2 sensor. The cars computer checks to see how well the cat is working but checking how fast the rear O2 sensor reacts to changes in the AFR that the front O2 sees. Basically if the cat is working efficiently it will burn up most of the stuff and the reading from the rear O2 will change very slowly compared to the front O2.

Of course when you add a high flow cat it typically has a smaller core with larger holes for less flow resistance, but therefore it normally is not as efficient at burning up emissions so some will pass through and the rear O2 will see that and set a code.

Possible fixes for this... A) get a slightly larger high flow cat that will have a longer core which will give it more time to burn the exhaust gases before hitting the rear O2, B) put some heat wrap around your downpipe to try and hold heat in and help the cat light off faster and burn more efficiently, or C) don't worry about it and ditch the rear O2 sensor. If you chose option C you'll need either a rear O2 simulator or a tuned PCM with the rear O2 codes deactivated. ;)


Yeah im ordering a mpracing pcm Tuesday already talked to mark about it
Thanks guys

young gun
08-09-2010, 11:57 AM
SES light is on for this code too. but for putting on my borla...Is it alright to leave it for awhile before attempting to fix this? just leaving it is just like getting a tuned pcm to remove the code but leaving it means i won't know if i get a SES light for something else... also if i end up getting a tuned pcm to fix this problem will i be alright passing inspection?

AaronGTR
08-09-2010, 03:00 PM
SES light is on for this code too. but for putting on my borla...Is it alright to leave it for awhile before attempting to fix this? just leaving it is just like getting a tuned pcm to remove the code but leaving it means i won't know if i get a SES light for something else... also if i end up getting a tuned pcm to fix this problem will i be alright passing inspection?


Putting on a cat-back exhaust WILL NOT cause this code. It only has to do with readings of the front and rear O2 sensors and how well the cat is working. If the stock cat is still there, then it is not from your borla. It's something wrong with the cat itself or the sensors.

young gun
08-09-2010, 08:41 PM
soooo nothing bad is happening right? (planning on getting cat and dp soon anyways)

AaronGTR
08-10-2010, 04:04 PM
Other than losing some HP if your cat is clogged? Not really. It doesn't go into a "limp mode" or anything like it will with a major malfunction, but I still wouldn't leave it for a real long time.

young gun
08-10-2010, 10:19 PM
ok thanks d00d. just need a little time before i get to it.