ok so i failed smog so i put my friends cat from his gsr onto my car. he didnt have a CEL on with his cat but now since i put his on my CEl came on. i reset my ecu a few times and nothing. im going crazy cuz i have to smog before i can reregister my car and i dont know why it threw a code. help!

 

Try a new rear o2 sensor.

 

but why would it just randomly go out when i put this other cat on?

 

bump! anyone have an opinion?