The reasons are as follows.

1. The volume on the car navigation system or mobile phone is not turned on.

2. The music playback programming of some mobile phones (such as Iphone) does not work with the docking code of some car models, so you can only answer calls but not listen to music.

3. The multimedia music of car Bluetooth is not turned on.

The solution is: Go to the phone's "Settings" - "Sound", find the "Media" option, turn up the "Media" volume, and use the car navigation system. Or it is recommended to change the Bluetooth playback frequency band, and it can be used normally.