Check engine code P0420

Monnk13

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Hi, I have a 2019 civic si with a PRL cobra cold air intake (street maf) and a hondata CARB +6 base tune. I installed the flashpro about a week ago. Today I received check engine code(p0420) saying there was an emissions problem. How is this possible? I have a street maf and a carb exempt tune. Has anyone had this problem, or can you offer a solution to this? I cleared the code once this morning, drove the car about 40 miles and it came back on. Any help is appreciated.
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Monnk13

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Iā€™ve had to clear the code 3 times in 24 hrs

Honda Civic 10th gen Check engine code P0420 A4A3B505-C0E0-4033-B369-940C344E848D


Honda Civic 10th gen Check engine code P0420 356F2710-D864-476A-BF7F-04C3756832D6
 

Naruske

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Make sure everything is secured tightly, all clamps are tight etc...
 

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Can also try to flash back to stock and see if the problem persists
 

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Have you swapped out your downpipe? P0420 is typically related to an aftermarket downpipe, not an intake.
 


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Monnk13

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Have you swapped out your downpipe? P0420 is typically related to an aftermarket downpipe, not an intake.
Stock down pipe. I did read up on aftermarket down pipe throwing the p0420 code. Thatā€™s why its so confusing getting that code with stock dp
 
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Monnk13

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Have you swapped out your downpipe? P0420 is typically related to an aftermarket downpipe, not an intake.
I flashed back to stock and the code popped back up 13 miles later. To add further confusion to my situation... after flashing back to stock, did a rolling start 0-60 to make sure turbo boost was back to normal, but it hit 18 psi during 1st gear and 15 psi in second. If I get the code again Iā€™m going to remove my PRL intake and see if I still get the code with stock air intake (I checked the clamps on the intake that can be seen without removing the skid plate...I was being lazy)
 

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If the problem persists on stock tune / stock intake / stock DP I think it's safe to say you could have a true problem with your cat or O2 sensor. I'd go to the dealer at that point (stock tune and bolt ons removed).
 
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Monnk13

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Can also try to flash back to stock and see if the problem persists
If the problem persists on stock tune / stock intake / stock DP I think it's safe to say you could have a true problem with your cat or O2 sensor. I'd go to the dealer at that point (stock tune and bolt ons removed).
that is the plan. Iā€™m going to give it a little time to see if it resolves. I read on the forums that some ā€˜19 civic Si owners kept getting the p0420 code and Honda had to do software updates to the ecu. Iā€™m hoping to avoid that because I have a flash pro. Just my luck, i buy a flash pro and a
Week later I seem to be having legitimate warranty issues (legitimate as in not from abusing car) that will force me to uninstall my CAI out of fear they will try to blame me for the issue (assuming my O2 sensor or converter are the reason for the CEL, my intake and flash pro would not be the cause for the failure)
 

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Did you by chance ever utilize the ā€œanti lagā€ feature?
 


SDSport6MT

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Other option is to go back to stock everything did you reach out to Hondata?
 
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Monnk13

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Other option is to go back to stock everything did you reach out to Hondata?
No I havenā€™t. I donā€™t think itā€™s the tune. I flashed back to stock and still received the check engine light. I think I have a bad O2 sensor (or wiring issue)
 

SDSport6MT

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No I havenā€™t. I donā€™t think itā€™s the tune. I flashed back to stock and still received the check engine light. I think I have a bad O2 sensor (or wiring issue)
If youā€™re flashed back to stock just take it to the dealer then.
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