NOx Sensor
– Two NOx sensors monitor the NOx
concentration within the exhaust gas. One sensor
before the DOC and one after the SCR module.
SCR Temperature Sensors
– The sensor monitors
the gas temperature entering the SCR. Also, a
second temperature sensor is located down stream
of the SCR. This sensor checks the temperature of
the gas that is leaving the SCR.
Ammonia Sensor
– The sensor monitors the
concentration of ammonia within the exhaust system
after the CEM.
Quality Sensor
– The quality sensor provides the
ECM with confirmation that the correct concentration
of DEF is present in the tank. If the tank is filled with a
different fluid which is not DEF, such as water or fuel
the sensor will detect this change in quality and raise
a fault. This fault will lead to an inducement and
engine derate.
The temperature sensor before DOC, NOx sensor,
SCR temperature sensors, and ammonia sensor all
connect with the engine ECM. If the signal from these
sensors is out of the set range, the ECM will trigger
an alarm for the operator.
Diesel Exhaust Fluid (DEF) System
Control
DEF Level Sensor
– The DEF level sensor signals
the ECM. The ECM determines the signal in order to
give a level reading of the volume of fluid in the tank.
DEF Temperature Sensor
– The sensor signals the
ECM. The ECM will determine the temperature of the
DEF within the tank from the signals sent. The
temperature of the DEF is important in order to keep
the DEF injector operation correctly.
Dosing Control Unit (DCU)
– The DCU controls the
injection of the DEF and will signal the ECM if the
injection has been interrupted.
The DEF level sensor, DEF temperature sensor, and
the Dosing control unit all connect with the engine
ECM. If the ECM determines that any of the signals
are out of the specified range, an alarm will be
triggered.
Testing
Turning the keyswitch to the ON position will check
the indicator lights on the control panel. All the
indicator lights will be illuminated for 2 seconds after
the keyswitch is operated. Replace suspect bulbs
immediately.
Refer to Troubleshooting for more information.
i05858075
Selective
Catalytic
Reduction
Warning
System
The
Selective
Catalytic
Reduction
(SCR)
system
is
a
system
used
to
reduce
NOx
emissions
from
the
engine.
Diesel
Exhaust
Fluid
(DEF)
is
pumped
from
the
DEF
tank
and
is
sprayed
into
the
exhaust
stream.
The
DEF
reacts
with
the
SCR
catalyst
to
reduce
NOx
and
leaves
a
nitrogen
and
water
vapor.
NOTICE
Stopping the engine immediately after the engine has
been working under load can result in overheating of
DEF system components.
Refer to the Operation and Maintenance Manual,
“Engine Stopping” procedure to allow the engine to
cool and to prevent excessive temperatures in the
turbocharger housing and the DEF injector.
NOTICE
Allow at least 2 minutes after the engine has stopped
before you turn the battery disconnect switch to OFF.
Disconnecting the battery power too soon will prevent
purging of the DEF lines after the engine is shut
down.
Warning Strategy
The engine ECM will have software enabled in order
to warn, derate, and only operate a low idle. This
software is in order to keep the engine emissions
complaint.
Warning Indicators
The warning indicators consist of a level gauge for
the DEF, a low-level lamp for the DEF, an emission
malfunction lamp, a warning lamp, a DEF quality
lamp, and the application stop lamp.
The DEF level gauge will only give an accurate
reading with the application on level ground.
SEBU9068-03
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