All Euro-6 engines are fitted with AdBlue system. This is a special liquid that reduces emissions when injected in the exhaust by the Engine Control Unit (ECU).  

The Adblue range varies depending on the driving style and other circumstances but a full AdBlue tank should last around 4000miles. 

If the AdBlue range reaches less than 1000 miles, the vehicle will warn you to fill up the AdBlue tank. 

You have to do this before the counter goes down to zero. The engine wont restart if the AdBlue range is 0 once switched off. 

Please make sure you fill up at least 5-7 litres if your range is 1000 miles or less. 

AdBlue can be purchased at most petrol stations and the cost is insignificant  compared to fuel.