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Operation—Operating the Machine
TX,SCR,OVERVIEW,2 -19-13JUL20-1/1
Selective Catalytic Reduction (SCR) System Overview
RG22427 —UN—14FEB13
SCR System
A—SCR Catalyst
B—DEF Dosing Injector
C—DEF Dosing Unit
D—DEF Tank Header Assembly
E—DEF Tank
IMPORTANT: Do not remove battery leads for at least
5 minutes after engine stops. The SCR system
automatically purges itself of diesel exhaust
uid (DEF) immediately after the engine is
stopped. If adequate time is not allowed for
lines to be purged, residual DEF can freeze
and possibly damage components of the SCR
system during cold-weather exposure.
In order to comply with national and local emission
requirements, this engine series contains a selective
catalytic reduction (SCR) system. The main components
of the SCR system include the SCR catalyst (A), DEF
dosing injector (B), DEF dosing unit (C), DEF tank header
assembly (D), and DEF tank (E). The SCR system is
effective at reducing the nitrogen oxides (NOx) emissions.
NOx is a major component of smog and acid rain.
During combustion, NOx molecules are formed in the
exhaust. DEF is injected into the exhaust stream before
the SCR catalyst. Through a chemical reaction in the
SCR, NOx is converted into nitrogen and water.
Water vapor is a normal by-product of combustion. During
cold-weather operation at low exhaust temperatures,
this water vapor can condense and resemble white
smoke from the exhaust. This will dissipate as operating
temperature increases and the water is further vaporized.
This situation is considered normal.
A DEF solution begins to crystallize and freeze at -11°C
(12°F). With climate temperatures that can range much
colder than this, DEF is expected to freeze in the DEF
tank. For this reason, the DEF tank contains a heating
element that provides rapid thawing of DEF upon start-up.
The heating element cycles to maintain uidity during
operation as needed. DEF is not dosed upon initial
start-up; therefore, it is not necessary to have liquid DEF
at cold start-up.
If DEF quality deteriorates and it is no longer within
specications, the engine can derate. DEF should be
crystal clear with a light ammonia smell. If DEF appears
cloudy, has a colored tint, or has a profound ammonia
smell, it is likely not within specication. A diagnostic
trouble code (DTC) is displayed, informing the operator to
replace the DEF. Upon replacement of DEF and operation
of the engine under load for a period of time or an
aftertreatment device regeneration, the code automatically
goes away with no required input from the operator.
2-3-16
112321
PN=167
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