O2 dummy sensor still throwing on and off CEL
 

My mazda 6 has gutted cats and the o2 sensor was dummied but it still throws a soft CEL on and off and its a pain in the ass. Im trying to sell it and i don't want it to turn people away bc of that CEL. Is there any way the dummy sensor could go bad? Or how can i prove its not a hard code and can still pass inspection.

A new upstream O2 sensor might cure it. The PCM is looking for a big difference in the upstream and downstream sensors. Your upstream might be reading too close to your dummy sensor. Or,like you say, it could be the dummy sensor that's bad.