A/V out to accesory issue

[r3dn3ck13]

I tried searching but not sure exactly what i need to be searching for. My Issue is that i have a Pionner AVIC-F900BT in my truck which has a ipod interface cord. You can control all music via the touchscreen. When i first got the iphone 4s the music played fine and all data transfered perfectly (playlists, songs, album art). Now 2 weeks later something changed and the music no longer plays. Album art and song info shows up on the screen but it wont play the song. When i manually select another song the screen goes blank. I know its the phone becuase i tried with a ipod nano and also a iphone 4 and they both work fine. i been searching online for a week and now im trying here. Does anyone have an idea what might be the problem? It worked fine and then nothing.. Im new to the Iphone and not a clue where to start.