does apple carplay use your data?

To be clear, the usage of CarPlay in and of itself does not use data.

i.e if you turn on your car, and connect your iPhone, and Car Play starts it does not use any data while it is connected.

Anything you do on it that requires an internet connection, such as using Maps, or streaming music from an online service would use data as it does on your iPhone without CarPlay.

Anything you do in CarPlay that requires Internet access will use data. Maps, streaming pandora, Apple Music, etc. CarPlay is just a simplified interface for your phone.

No.