That is quite odd. Especially if it works in the home (the same cord(s)). Try a simple reboot of the phone and see if that resolves it. Sometimes, if people never turn off their phone, this can happen.
If that doesn't do it, I would try using a different connector for the vehicle and see if it works. If it still doesn't work for you, but does for him, it may be phone related (even though it doesn't seem so). I would check to make sure your port on the phone isn't damaged, loose, or has dust, etc., in it. Then if the problem persists, and you are under warranty still, then I would contact the manufacturer.