What is legacy def?

"Legacy DEF" refers to Diesel Exhaust Fluid (DEF) that was sold before the implementation of the ISO 22241 specification in 2010. The ISO 22241 specification sets standards for the quality, composition, testing, and storage of DEF. Legacy DEF may not meet the requirements of the ISO 22241 specification, leading to potential issues with engine performance, emissions control, and SCR (Selective Catalytic Reduction) systems. Vehicles and equipment that require DEF should only use DEF that meets the ISO 22241 specification to ensure optimal performance and compliance with regulations.