During vehicle operation, SCR systems are designed to provide heating for the DEF tank and supply lines. If DEF freezes when the vehicle is shut down, start up and normal operation of the vehicle will not be inhibited. The SCR heating system is designed to quickly return the DEF to liquid form and the operation of the vehicle will not be affected.
A 32.5% solution of DEF will begin to crystallize and freeze at 12 degrees F (-11 deg C). Freezing does not harm the quality of the DEF solution. Upon thawing, DEF will perform as required.