I know, vague title, but my question is. Has anyone had a service engine soon light come on after a loud rattle was heard on start up? I will clarify. My wife has an 07 MCSC that the light came on and I found that the rattle was a loose O2 sensor behind the cat. I tightened, and rattle gone, but light not. My question is, will the light go away, or will I need to have it reset. Thanks in advance for any help.
Jon

 

More than likely you will have to reset the codes. They usually do not reset themselves.