Does an after market cat make the check engine light come on and how do you make it not come on.

 

A real, aftermarket OEM spec replacement cat (like one a muffler shop would put on) will not set an SES light.

If you're planning on doing a high flow cat, or cat delete it will likely come on.

To turn it off you need to either:

A)buy an O2 simulator for the rear O2 and eliminate it
B)have someone tune your pcm to eliminate the code.

 

ok thanks thats what i needed to know