Mary got a new Scion automobile and she can connect her phone to it, but it doesn't work right. She can't hear the turn by turn directions when she connects her Samsung Galaxy Note 4 to it. Leo says that there is a setting for it to play over the music. Doctor Mom in the chatroom says she had a similar problem and she says to start over with the Scion. Forget the pair in her Scion Bluetooth settings, and then repair it. Leo also says to look in the navigation settings in Google Maps to change the volume on the voice settings. There's also a 'mute' checkbox there.
Here are a couple of pages for more information about it:
There's also a free app called A2DP Volume, which may help.