Not every car unit will read dvd mp3 and when they do they usually have rules on the structure the music is in. They might have a maximum file number they can see as in if you burn a disk with a 1000 mp3's all in the root it wont read them. It might also have a restriction on the depth of directories it can read. They aren't all the same rules either so your going to have to dig the manual out to find out if yours can play them and what the rules are. Also check your closing the disk off as some cant read open disks, infact I have seen some computers that cant read open disks as well.