my car lately when I punch it and I go ahead and park It smells kind of bad like its coming from the exhaust.My ses light in the past 4 months have come on and off.Right now it is off.GM currently put new cats.What do you think it is.

 

It could be burning oil

 

Do you remember what the SES light was for (what code)?

 

If the light has come on since the cats were replaced I'd get the car scanned, even with the light off it might still be stored as a "history" code.