The volume of the tank on your GL-class 33,4L.
In case the level of AdBlue® drops to the reserve level of 3.0L, which corresponds to a mileage of 1500 miles, the message “Add AdBlue® see instruction manual" will appear on the dashboard. The warning message disappears 1 minute after the fill up if you drive faster than 10miles/h. If the level reaches its minimum, the message "top-up AdBlue® mileage: ...km" is to be seen on the dial switch indicating to you your remaining mileage. In case of a breakdown, the message "Top-up with AdBlue®, restart impossible" shows up to ask you you to top up. If your tank is completely empty, pour a minimum of 3,5 L to switch the warning off.
As soon as your tank is empty and that you turn the engine off, you cannot restart the car. If the engine is still running, you are able to drive to a service station. After fill up, turn the ignition on for 60 minutes and start the engine.
This information can vary on some vehicles of the same model in relation to the options chosen by the manufacturer.