The volume of the tank on your A5 is 17L.
In case your AdBlue® tanks reaches a remaining mileage of 1500 miles, a warning light appears on the dashboard. An audio signal sounds to warn you. Below 650 miles of remaining mileage, an AdBlue® warning is visible on the driver's screen. An alarm signal can be heard and a message warns the drivers that restarting the car is impossible once the tank is empty. When the tank is empty, a message is displayed along with three audio signals. To extinguish the AdBlue® warning when the tank is empty, pour at least 5,7L AdBlue® in the tank.
When your warning reaches 0 miles, restarting the car is not possible anymore. If your engine is till running, you can drive to the next service station. If the car does immediately start after the AdBlue® top-up, you need to wait for two minutes for the system to detect it. If the tank of AdBlue® is completely empty, you need to turn the ignition on for around 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.