I got the Service engine light after i did the tune up on my mustang, does anyone knows, if the tune up had something to do with the light??? or i should check it out???
You could either go to a mechanic, or, allegedly, small auto parts stores [Like Autozone and such] will run the diagnostic for free and give you the codes. But, the Mechanic will tell you which codes mean what, and what to replace.
But, if you get the codes you can run a search online, find out what could be the reasons for the code and replace it that way-- it's potentially cheaper. But, you can mis-diagnose it and replace the wrong thing.