i just put headers to a "test pipe" and 2 1/4 apex N1 exhaust itts a 00 prelude 5-speed tranny and my CEL keeps coming on its a p0420 code (catalyst effeciency) is that because of the test pipe on obd2 is there a way to reprogram the ecu to acknowledge the upgrade and is this hurting my performence should i just put my stock cat back

 

yeah mine use to do the same thing. u need a cat for obd2 cars. or just get a cat to use when going threw emmisons.

 

well i dont have any emmission test were i live so having this test pipe is worse then the stock cat?