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Discussion Starter #1
So I just got a Fullrace 3" catless downpipe installed on my 2013 civic si coupe. Now I know since its catless that it will throw a CEL and to my knowledge if you use a flashpro to disable the "P0420 catalytic efficiency error" then the CEL should go away , right? Well I did that and when I first cranked up the car it showed no CEL, I even ran an OBDII diagnostic with flashpro and everything seemed to be in order. However when I started the car up for a second time it showed a CEL and upon running another OBDII diagnostic it was caused by the feature that I had diabled. I'm new to modifying cars but I try to do my research and I cant figure it out. Thanks in advance, if you need more info just ask.
 

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Try disabling the secondary O2 sensor

You can find that under "closed loop"


Or get a defouler for the secondary O2. You'll need that for emissions anyway
 

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Discussion Starter #3 (Edited)
I disabled the secondary o2 sensor and it worked thanks. I don't need a defouler because I live in Florida so i don't have to worry about inspection :cool: . Thanks for the help.
 
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