For those who are having problems with Nokia 6 not being able to connect to the car head unit using Android auto, below is the solution:
1. Please ensure all the relevant softwares are up to date
2. Use a high quality USB cable. Amazon basics. Sony. Ivoltaa cables are good enough.
3. Turn on USB debugging on your phone.
4. Go to settings - battery - battery activity manager - turn on Android auto & maps from the list below.
5 . Reboot the device and you are good to go.