Is installing a catless Invidia Midpipe a bad idea when it comes to check engine lights and thrown o2 sensors? I hear that the cats in the midpipe are secondary, knowing this, are the secondary cats monitored by o2 sensors? I guess the question im trying to ask is will i get any lights on if i change the midpipe, and will the service guys at the dealership get all worked up about 2 missing cats?

 

I just had an Apexi Midpipe installed on my '15 IS350 and had no CEL since the o2 sensor is located before the secondary cats. My guess the only reason you would a throw code is if you damaged the sensor or twisted the wires during install.