Hi there SanDiegoDel,
Thank you for using the Apple Support Communities. I understand you're not able to hear messages as read through CarPlay.
To clarify, are you finding that there are no volume controls for reading Messages? Or are you able to adjust the volume but find it doesn't make an audible change? It's possible that a setting specific to the vehicle stereo is causing this behavior, but there are some steps you can try on the iPhone end that might be helpful.
To start, check out the "Get help" section of this link: How to use CarPlay with your iPhone. This will cover a few helpful steps, including updating your device, restarting, and forgetting and re-establishing the CarPlay connection.
I hope this helps!
Take care.