The volume of the tank on your Q7 is 24L.
When less than 1500 miles of mileage are remaining, a signal appears on your dashboard warning you to fill up. An audio signal sound is used to warn you. Below 650 miles, a message warns you that restarting your car will be impossible once the tank is empty. When the tank is completely empty, a message is displayed along with three audio signals. When the tank is completely empty, pour at least 5,7L of AdBlue® in the tank to turn the AdBlue® warning off. Leave the key in the ignition for two minutes without turning the engine on.
When your tank is completely empty, you will not be able to restart the engine after it has stopped. You need to fill up with AdBlue®. If the car does not start immediately, you may have to wait two minutes for the system to taken into account the AdBlue® top up. If the AdBlue® tank is empty and mileage shows 0 miles on the driver's information system screen, you have to turn the ignition on for about 15 seconds and then start the engine.
This information can vary on some vehicles of the same model in relation to the options chosen by the manufacturer.