Operators are fitting emulators to switch off the diesel exhaust fluid, which many of us refer to by the brand name Adblue. The authorities are clamping down on the use of these cheat devices. The only way a driver will know if their vehicle is fitted with such a device is by observing that the DEF gauge does not move after a day or so. Some vehicles when fill with DEF will go for several days before the gauge will move off full. If the vehicle is driven by a number of drivers it would be lightly that a driver may never notice the vehicle has a cheat device fitted.  

In computing, an emulator is hardware or software that enables one computer system (called the host) to behave like another computer system (called the guest). An emulator typically enables the host system to run software or use peripheral devices designed for the guest system. An emulator can be fitted to a truck or bus and tell the vehicle that the system is operating as it should, even if no Diesel Exhaust Fluid (DEF)

DEF is an aqueous urea solution made with 32.5% urea and 67.5% deionized water. It is used as a consumable in selective catalytic reduction (SCR) in order to lower NOx concentration in the diesel exhaust emissions from diesel engines.
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