DEF is a reactant that is necessary for the SCR system to function. It is a carefully blended aqueous urea solution 32.5% high purity urea and 67.5% deionized water.
You can go approximately 800 miles on 1 gallon of DEF.
Any diesel vehicle later than 2010.
DEF needs to be stored out of the sunlight in temperatures between 40-80 degrees. Doing this, it should last about 2 years.