https://support.google.com/androidauto/answer/6348190?hl=en
hope this helps
"Android Auto App not Working
Unplug your phone from the car.
Open the Android Auto app on your phone.
Select Menu Settings Connected cars.
Uncheck the box next to the "Add new cars to Android Auto" setting.
Try plugging your phone into the car again.
Make sure the car is compatible with Android Auto and that Android Auto is turned on."