Well I'm not all that familiar with cars and their workings but I'm pretty sure the reason it isn't playing could be either that you aren't recognizing it or that its saved in teh wrong format and also is teh music in a subfolder of the usb.. because if so then it could be not finding it since a stereo isn't as complex as a computer to look for files it just hopes that the file is there.. But try putting all the files on the usb directly and not in a subfolder.. or you can simple change the file extension type to something such as .mp3 or .wma... goodluck ^^