To trouble shoot you change the iPod out and if it still fails the vehicle needs repair. I cringe at how much to fix that.
Maybe it would be cheaper to change the car's audio system?
ipod classic 2009, 160GB, has stopped playing via Car's USB, I have reset and reformatted and contacted Apple help line. it used to play, now only recognises and displays but wont play. it plays on imac computer and other USB devices, but have tried other vehicles USB ports with same result. ipod software version 2.0.4