The Selective Catalytic Reduction (SCR) catalyst converts a mixture of nitrogen oxides and Diesel Exhaust Fluid
(DEF) into nitrogen and water. DEF is pressurized by a pump and is then sprayed into the exhaust between the
Diesel Oxidation Catalyst (DOC) / Diesel Particulate Filter (DPF) and the SCR catalysts within the mixing
chamber.
Description and Operation of the Diesel Exhaust Fluid Flow
Diesel Exhaust Fluid (DEF) is stored in the onboard DEF tank manufactured by the vehicle Original Equipment
Manufacturer (OEM). DEF is pulled through the DEF tank header to the DEF pump. DEF is pumped to the dosing
unit at 10 bar (145 psi) and is injected into the aftertreatment. DEF circulates back to the DEF tank from the
dosing unit.
Description and Operation of the Diesel Exhaust Fluid Heating
Diesel Exhaust Fluid (DEF) is fluid that can freeze and must be heated in cold ambient conditions. The DEF tank
(1) and DEF pump module (2) use coolant from the engine to heat DEF. Coolant flows from the coolant collector
on the engine through the coolant hose (3) to the coolant valve (6). The coolant valve solenoid is controlled by the
ACM. The ACM regulates coolant flow to thaw and maintain temperatures above the DEF freezing point of minus
11°C (12°F). From the coolant valve, the coolant flows through the DEF tank header (4) into the DEF tank.
Coolant flows out of the DEF tank through the coolant hose to the DEF pump module. From the DEF pump
module, coolant flows back to the engine (5).
