The volume of the tank on your Discovery is 17,8L.
The remaining AdBlue® autonomy can be checked anytime on the "message center" on the dashboard. A first signal warns on the necessity to fill-up with AdBlue® 1500 miles before the tank is empty, followed by a second signal when only 900 miles of autonomy remain. A third warning indicates that there are only 550 miles remaining and that the tank must be filled, at risk of the vehicle being unable to restart. The last warning indicates that only 90 miles of autonomy remain. In order to turn off the warning when your tank is empty, you have to fill your tank with at least two cans of 1,89L or a can of 5L. If the warning light is on even after you have filled up, you have to start the engine, wait for 30 seconds and stop it. Repeat this action three times.
When the tank is empty, you can drive until you turn off your engine. Once your tank is completely empty, you cannot restart the engine.
This information can vary on some vehicles of the same model in relation to the options chosen by the manufacturer.