Hot Shot's Secret Premium DEFender is engineered to clean and prevent DEF crystal buildup. Harmful deposits in the SCR system can reduce performance, increase fuel use, and lead to costly repairs or downtime. Restore performance while protecting the injector, sending unit, tank and more. Use at each time refilling DEF to prevent white crystallization deposits from forming. Triple-filtered for purity. Ash and dye-free formula guaranteed not to void the manufacturer's warranty when used as directed.