Are you trying to use audio out via the jack socket to connect to an aux input? Does the socket work with headphones? Disabling aux output seems to be something that came in with Marshmallow and is an Android thing. No one seems to know why, though it would be likely to be something to do with security (a possible risk of malware feeding back in, maybe from a connected car?)
. The only way to connect now seems to be Bluetooth. If you can get a receiver that connects to the vehicle's jack input, that's probably your best bet.
