When I got my o/r pipe about two months ago my SES light came on, got it checked just to make sure and it was definately that so I've been driving around with it on ever since. Today i noticed it wasn't on anymore, and I didn't do anything to the car.... whats the deal with that?
Trust me it will come back on. My sensors were throwing random codes even with the stock pipe. Those things are stupid like that...you should get the MILs anyway.