Will aftermarket CAT set off my check engine light?

I was wondering if an aftermarket Catalitic Converter set off my check engine light because I wouldnt have the "after CAT sensor" anymore?
 
 
Thanks for any help
 
 
Matthew 

probably, ive seen this talked about before and you can have it put in. they say if you have the sensor in and it throws a CEL, you can put a washer on the threads to back the sensor out a little and it apparently helps. not certain though never done this myself
-good luck

probably, ive seen this talked about before and you can have it put in. they say if you have the sensor in and it throws a CEL, you can put a washer on the threads to back the sensor out a little and it apparently helps. not certain though never done this myself
-good luck