Hey, I just bought a 2004 cts and see this audio input and cable next to the ashtray. I have an ipod nano and would like to use it in the car. How do I make the nano compatible with the audio input or "that other cable"?

 

The check engine light on my 04 cts came on half way through a 5 hour drive. Went off driving around the following day. Two days later it came back on my that 5 hour drive back home. Still on the next day. I made sure the gas cap is on correctly. Should I wait to see if it goes off again or have the dealer do a diagnostic test? Can an auto parts store do computer diagnotics? Less cost than dealer?