This is Designed to be used as a one click Home screen shortcut Widget.
When launched, this Flow will enable Bluetooth and attempt to connect to your paired Bluetooth vehicle. Once connected It will adjust the volume on your phone to maximum. Your phone will stay connected until your vehicle's Bluetooth is off. Then your volume will be set to 70.
This Flow will also handle text messages. If someone sends you a text message while you are driving it will [auto reply] back to them with a custom message.
For this to work correctly, you must Launch this AFTER you start your vehicle. How long after may vary depending on your vehicles BT activation after start. You will also need to select your paired device in the "Connect BT device" Block. If your phone's BT turns off before connecting to your vehical, you may need to adjust the "Delay" Block to give it more time to connect.
If you don't want the SMS auto reply function just delete the "Fork" Block and reattach the fiber.
To create your "Home screen shortcut" Widget go into the "Flow Beginning" Block and click "Homescreen shortcut". It will appear on one of your Home screens.
Works on Lollipop 5.1