Since I don't have the ability to test it, it may be best to go to an Apple Store, or contact AppleCare by phone. It figures that the car manufacturers don't have much knowledge about it.
I have heard that many people have this issue. Here's quote from a post in another forum I found that you could try:
"
When your iPhone is connected via Bluetooth to your vehicle, you should be able to access the Control Center on your iPhone by swiping up from the bottom of the screen. Afterwards, the name of your car or car's feature, should be visible just above the bottom row of icons. For those with an Apple TV, "AirPlay" will be displayed there. Anyway, if you tap on the name of your car, you will see "iPhone" as another choice to select. If you opt to select "iPhone", your text and email notifications will be heard through the iPhone's speakers whereas any call notifications will be heard via the vehicle's speakers. This is a workaround that allows you to play your radio in your car and still hear the aforementioned notifications."
C