SCR CRYSTAL CLEAN™ Diesel DEF SCR Emissions System Cleaner is a propriety blend of DEF (Diesel Exhaust Fluid) compatible cleaning agents and surfactant detergents specifically designed to be safe to use and work on SCR (Selective Catalyst Reduction) systems. SCR Crystal Clean gives a cleaning effect on the entire SCR system by working to dissolve and solidify the white crystal deposits that form in the tank, pump, lines, injector and mixer. These deposits can interfere with the normal operation of the system and engine, to the point that they vehicle will become no longer drivable. This process restores their function and with regular use maintains efficiency. UREA Crystallization Cleaner. Clears P218F and Other OBD Codes. Restores DEF and SCR System. Cleans DEF Injecotr, Sender and Pump.