The volume of the tank on your Touareg is 20L.
Below 1500 miles, a message is displayed every 60 miles, until only an autonomy of 1000 miles remains. Below 1000 miles, a message is displayed every 30 miles, with an audible signal and an orange light. When the AdBlue® tank is completely empty, the indicator light becomes red.
If the indicator light turns red, and the ignition is turned off, you will not be able to start the vehicle. You have to fill up to be able to restart the engine.
This information can vary on some vehicles of the same model in relation to the options chosen by the manufacturer.