Maybe it's because the Bluetooth stereo is not paired. You can try to hold down the volume adjustment button until the on-board system is turned off, wait a few seconds, and then turn it on.

The following is an introduction of carplay:

CarPlay is an in-vehicle system released by Apple in the United States, connecting users' iOS? Seamless integration of devices, iOS experience and dashboard system.

CarPlay only supports iPhone with Lightning interface. Although iPad already supports this interface, Apple has not listed iPad as a hardware device supported by CarPlay. 201June 13, Apple said at the WWDC Developers Conference that CarPlay, the company's intelligent in-vehicle system, will be updated together with iOS 10 to become the best partner of the new version of Apple Maps and Siri.

In 20 13, apple announced its entry into the automotive field and announced its in-vehicle iOS plan. IOS in the car? After the plan was announced, Apple attached great importance to this system. 20 13, 1 1, Apple also established a shell company called CarPlay Enterprises. This company has no obvious connection with Apple, and its main task is to submit CarPlay's trademark application.

Refer to Baidu Encyclopedia -Carplay for the above information.