Why on earth do companies send drivers out in vehicles that use Ad blue or DEF as it is known over here ? If you have no idea how the system works read the [zb] manual before you do. The first truck I had with the system I looked at the manual and found out everything I needed to know, if there is no manual ask, there can be no shame in asking for advice rather than breaking down because the engine has shut down when you run out of it. It’s quite simple really, every time you fill with fuel top up the DEF (ad blue). If you ruin the engine your boss will be really angry and you will look like the idiot you show yourself to be.