One of the most common causes, and easiest to remedy, is a loose gas cap. Make sure the mating surfaces are clean and the cap is securely tightened. If that is the cause the light will go out by itself. If not, most major auto parts stores will read the code for free. It only takes a few minutes. Post the code here and we can walk you through it.
2005 SL AWD, Platinum
-OEM HID conversion & HID fogs
-OEM iPod interface
-Upgraded (non-Bose) speakers - Pioneer TS-A1702C & TS-G1643R
-Muth signal mirrors
-Valley Industries hitch and wiring harness
-Aluminum fuel tank shields