The gallon bottle is the practical size for topping off between services rather than refilling an empty tank. DEF is injected ahead of the selective catalytic reduction catalyst, where it converts nitrogen oxides into nitrogen and water vapor. Let the tank run dry and the engine controller will derate power and eventually refuse to restart.

Fluid Specifications:

• For selective catalytic reduction systems on select diesel applications.
• Converts nitrogen oxides in the exhaust into nitrogen and water vapor.
• Supplied ready to use. Do not dilute.
• 1 gallon bottle.
• Store out of direct sunlight and above freezing.