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November, 2019

with a biodiesel content up to 20% by volume may
be used (e.g., named B20). Look for the TOP
TIER Diesel Fuel Logo.
– Do not use diesel fuel with more than 15 ppm
Sulfur.
– Do Not Use Non-Highway Diesel Fuel.
Glow Plugs: The engine utilizes eight ceramic
glow plugs. Compared to conventional glow plugs,
ceramic glow plugs enable greater efficiency
through higher temperature capability and faster
preheating time. However, ceramic glow plugs are
much more sensitive to damage than conventional
glow plugs. Damage can occur to the glow plug
and not be visible, causing future engine failure.
Therefore, ceramic glow plugs are considered
one-time-use. Be sure to discard and replace with
NEW whenever a ceramic glow plug is removed
from the cylinder head. If the cylinder head is ever
removed with the ceramic glow plugs, the ceramic
glow plugs must all be replaced with new.
Whenever installing a new ceramic glow plug,
clean the glow plug bore with a proper tool as
outlined in the service procedure. Carbon build-up
in the glow plug bore can damage the ceramic
glow plugs.
Governed Speed: 2900 RPM
Horsepower: 350 hp (257 kW) @ 2700 RPM.
Torque: 700 lb-ft (949 Nm) @ 1600 RPM.
Intake Airflow Valve: The intake airflow valve is
a throttle plate actuator and is used to achieve
high exhaust gas recirculation rates. It increases
the pressure difference between exhaust and
intake so that the appropriate exhaust quantity
can be mixed with the intake air.
Maximum Braking Speed: 4,800 RPM.
Maximum Powered Speed: 3,450 RPM.
Oil Cooler: The oil cooler lowers engine
temperature by cooling the oil with engine coolant.
Engine coolant is directed from the water pump to
the oil cooler by a coolant tube. The oil filter
attaches directly to the oil cooler.
Oil Pump: The oil pump is gear driven directly
from the crankshaft. The oil pump drive gear is a
slip fit to the crankshaft.

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Bulletin No.: 18-NA-366

Piston: The pistons are a full-floating design. The
piston pins are a slip fit in the bronze bushed
connecting rod and are retained in the piston by
round wire retainers. The pistons have a piston
cooling oil channel cast inside of the piston. These
cooling oil channels utilize an oil jet located at the
bottom of the cylinder bore to direct oil into the
piston channel. There are two compression rings
and one oil control ring. There is a groove
machined into the pistons between the first and
second compression rings. This groove reduces
compression ring leakage by providing an empty
space for expanding gases, reducing the
combustion gas pressure on the second
compression ring.
Turbocharger: The turbocharger is water cooled
for improved durability. It is a variable vane style.
The pitch of the turbine vanes can be changed by
ECM command to meet varying conditions.
Upper Oil Pan: A single piece cast aluminum
upper oil pan contributes to crankshaft and block
rigidity while reducing overall weight.
Valvetrain: The engine utilizes a mechanical
roller lifter for valve operation. One rocker arm
operates two valves simultaneously through a
valve bridge.
Water Pump: The water pump is gear driven for
improved reliability.

Elevated Idle
The engine has a cold temperature high idle feature
which elevates the engine idle speed from base idle to
1050 to 1100 RPM when outside temperatures are
colder than 32°F (0°C), and the engine coolant
temperature (ECT) is colder than 150°F (65°C). This
feature enhances heater performance by increasing the
ECT faster.
Engine Block Heater
If equipped, the engine block heater can provide easier
starting and better fuel economy during the engine
warm-up period in weather conditions that are colder
than 0°F (−18°C). Vehicles with an engine block heater
should be plugged in at least four hours before starting.
An internal thermostat in the plug-end of the cord may
exist, which will prevent engine block heater operation
at temperatures warmer than 0°F (−18°C).

Bulletin No.: 18-NA-366

November, 2019

Page 11

Fuel System Overview
L5D Fuel System Diagram

5135268

Legend
(1)
(2)
(3)
(4)
(5)
(6)
(7)
(8)

Secondary Fuel Tank (if equipped)
Fuel Filter with Water in Fuel Sensor
Fuel Heater
Fuel Temperature Sensor
Fuel Pressure Sensor
Exhaust Aftertreatment Fuel Injector (not
equipped on the L5D)
Dual Fuel Rail Pressure Sensor
(Contains Fuel Rail Pressure Sensor 1
and Fuel Rail Pressure Sensor 2)
Fuel Rail Assembly

The primary fuel tank and secondary fuel tank (if
equipped) stores the fuel supply. A fuel transfer pump is
located in the secondary fuel tank to transfer fuel to the
primary tank. The primary fuel tank contains a 3–phase
electric fuel pump that is controlled by the fuel pump
driver control module and ECM. Fuel is pumped from
the primary fuel tank through the fuel feed line to the
fuel filter assembly. The fuel filter assembly consists of
a fuel filter/water separator, fuel heater, fuel
temperature sensor, and a water in fuel sensor. Fuel
flows out of the fuel filter assembly through the rear fuel
feed pipe and past the fuel pressure sensor to the fuel
injection pump. High pressure fuel is supplied through
the high pressure fuel line to the fuel rails and then

(9)
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(12)
(13)
(14)
(15)
(16)

Fuel Rail Pressure Regulator 2
Fuel Pressure Regulator 1 (Located in
Fuel Injection Pump)
Fuel Injection Pump
Fuel Injectors
Primary Fuel Tank
Electric 3–Phase Fuel Pump
Fuel Transfer Pump (if equipped with
secondary tank)
Fuel Pump Driver Control Module

through the fuel injector lines to the fuel injectors. High
pressure fuel is controlled by the ECM, Fuel Pressure
Regulator 1 and Fuel Pressure Regulator 2. Excess fuel
returns to the fuel tank through the fuel return pipes.
Exhaust Aftertreatment Uses Post Injection
The engine uses post combustion injection through the
engine fuel injectors to increase the exhaust gas
temperature as needed for regeneration. It does not
use an HC Injector.

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November, 2019

Bulletin No.: 18-NA-366

Engine Oil

Exhaust Brake

Specification
Engine oil with the letters CJ-4 or CK-4 are required for
the Duramax® 6.6L diesel engine. The CJ-4 or CK-4
designation can appear either alone or in combination
with other American Petroleum Institute (API)
designations, such as API CJ-4/SL. These letters show
API levels of quality.

Operation
The exhaust brake can be used to enhance the vehicle
brake system and reduce brake lining wear. Downshifts
may be automatically selected to increase engine
speed, which increases the effectiveness of the
exhaust brake. The number of downshifts selected is
determined by the length of time the brakes are applied
and the rate the vehicle is slowing. The system delivers
the correct amount of braking to assist in vehicle
control. The heavier the vehicle load, the more active
the engine exhaust brake will be. Automatic downshifts
will not occur if the vehicle is in Range Selection Mode.

American Petroleum Institute (API) Symbol

Activation

5123610

This doughnut-shaped logo (symbol) is used on most
oil containers to help you select the correct oil. It means
that the oil has been certified by the American
Petroleum Institute. Look for this on the oil container,
and use only those oils that display this logo.
Caution: Use only engine oils that have the
designation CJ-4 or CK-4 for the diesel engine.
Failure to use the recommended oil can damage the
DPF and result in engine damage not covered by
the vehicle warranty.
Viscosity Grade
Use SAE 15W-40 viscosity grade engine oil. When it is
very cold, below 0°F (−18°C), use SAE 5W-40 to
improve cold starting. These numbers on the oil
container show its viscosity, or thickness.

5182573

The exhaust brake only activates when the
transmission torque converter is locked. This can vary
based on vehicle speed, gear, and load. To activate the
system, press the exhaust brake switch in the control
panel. A light in the switch will turn ON when the
exhaust brake is activated. The DIC displays the
message EXHAUST BRAKE ON for approximately
three seconds, then clears. To turn the brake OFF,
press the exhaust brake switch a second time. The DIC
displays the message EXHAUST BRAKE OFF for
approximately three seconds, then clears. The switch
must be pressed at each vehicle start for the system to
be active.

Exhaust Aftertreatment System
Tip: Depending on the Service Information being
referenced by the Technician, such as Diagnostic
Trouble Codes, Description and Operation, Component
Replacement Procedures, Power and Signal Master
Electrical Component List, Bulletins and the Electronic
Parts Catalog, component names for the various parts
in the Exhaust Aftertreatment System will vary.

Bulletin No.: 18-NA-366

November, 2019

Page 13

L5D Emission Control System Architecture

5138795

Legend
(1)
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NOx Sensor 1 (B195A Nitrogen Oxides
Sensor 1)
EGT Sensor 2 (B131B Exhaust
Temperature Sensor 2)
Differential Pressure Sensor (B154
Diesel Particulate Filter Exhaust
Differential Pressure Sensor)
EGT Sensor 4 (B131D Exhaust
Temperature Sensor 4)
DEF Injector (Q61 Reductant Injector)

Exhaust Aftertreatment System
Diesel Fuel Requirements
Notice:
• Use Ultra Low Sulfur Diesel Fuel (ULSD) only.
Do Not use a diesel blend containing more than
20% biodiesel by volume.
• Do Not Use Non-Highway Fuel. Fuel labeled as
off road or non-highway is typically very high in
sulfur content and will damage the emission
control system. Non-highway fuel is not
intended for use in on-highway vehicles and
does not have the fuel properties needed by the
Duramax® Exhaust Aftertreatment System to
properly function.

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EGT Sensor 5 (B131E Exhaust
Temperature Sensor 5)
NOx Sensor 2 (B195B Nitrogen Oxides
Sensor 2)
Particulate Matter Sensor (B136 Exhaust
Particulate Matter Sensor)
EGT Sensor 3 (B131C Exhaust
Temperature Sensor 3)
EGT Sensor 1 (B131A Exhaust
Temperature Sensor 1)

Overview
The diesel exhaust aftertreatment system is designed
to reduce the levels of hydrocarbons (HC), carbon
monoxide (CO), oxides of nitrogen (NOx), and
particulate matter remaining in the vehicle’s exhaust
gases. Reducing these pollutants to acceptable levels
is achieved through a 3 stage process as follows:
1. The close coupled Diesel Oxidation Catalyst
(DOC) stage
2. The Diesel Particulate Filter (DPF) stage
3. The Selective Catalyst Reduction (SCR) stage

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November, 2019

Component Function
The main components function as follows:
– The Close Coupled Diesel Oxidation Catalyst (DOC)
removes exhaust HC and CO through an oxidation
process.
– Particulate Matter (PM) consisting of extremely small
particles of carbon remaining after combustion are
removed from the exhaust gas by the porous barrier
in the Diesel Particulate Filter (DPF) which lets the
gases pass through and retains the particulates.
– Diesel Exhaust Fluid (DEF), is injected into the
exhaust gases prior to entering the SCR. Within the
SCR, NOx is converted to nitrogen (N2) and water
vapor (H2O) through a catalytic reduction fueled by
the injected DEF. The SCR is a single assembly
canister, consisting of two separate SCR bricks
which are separated by a small space in which EGT
Sensor 5 resides.

Close Coupled Diesel Oxidation
Catalyst (Oxidation Catalytic Converter)
Close Coupled Diesel Oxidation Catalyst (Oxidation
Catalytic Converter) Overview
The close coupled DOC functions much like the
catalytic converter used with gasoline fueled engines.
As with all catalytic converters, the DOC must be hot in
order to effectively convert the exhaust HC and CO into
CO2 and H2O. On cold starts, the exhaust gases are
not hot enough to create temperatures within the DOC
high enough to support full HC and CO conversion. The
temperature at which conversion starts to occur is
known as light-off. Proper DOC function requires the
use of ultra-low sulfur diesel (ULSD) fuel containing
less than 15 parts-per-million (ppm) sulfur. Levels
above 15 ppm will reduce catalyst efficiency and
eventually result in poor driveability and one or more
DTCs being set.

Bulletin No.: 18-NA-366

consisting of thousands of porous cells. Half of the cells
are open at the filter inlet but are capped at the filter
outlet. The other half of the cells are capped at the filter
inlet and open at the filter outlet. This forces the
particulate-laden exhaust gases through the porous
walls of the inlet cells into the adjacent outlet cells
trapping the particulate matter. The DPF is capable of
removing more than 90% of particulate matter, or soot
carried in the exhaust gases.
Differential Pressure Sensor (Diesel Particulate
Filter Exhaust Differential Pressure Sensor)
Operation
Pressure connections at the DPF inlet and outlet allow
the Differential Pressure Sensor (DPS) to measure the
pressure drop across the DPF. The pressure drop
increases as trapped soot collects in the cells of the
DPF during vehicle operation. The rate at which soot
collects varies with the power demands placed on the
engine. If left unchecked, the increasing backpressure
will eventually result in a driveability problem. There are
two sensing elements in the Differential Pressure
Sensor (DPS), one for the upstream side of the DPF,
and the other for the downstream side. Pressure from
each side of the DPF is applied to the bottom side of a
silicon diaphragm in each sensing element;
atmospheric pressure is applied to the top side of each
diaphragm. Relative pressure differences in each
sensing element is converted to a voltage (V1 & V2).
The difference in these voltages is sent to the ECM. As
the DPF becomes clogged, the pressure on the
upstream side increases because of back pressure due
to the restriction of the exhaust gas flow through
the DPF.

DOC Operation
In addition to reducing emissions, the DOC also
generates the exhaust heat needed by the SCR stage
to perform its function. Exhaust gas temperature
sensors are located upstream and downstream of the
DOC. By monitoring the temperature differential
between these two sensors, the ECM is able to confirm
DOC light-off. Light-off is confirmed by a DOC output
temperature that is greater than its input temperature.
In order to generate the high exhaust temperatures
needed for regeneration, the aftertreatment system
increases exhaust temperatures by injecting additional
diesel fuel into the post combustion process.

Diesel Particulate Filter (Exhaust Particulate Filter)
Regeneration
Over time, the soot trapped on the cell walls acts to
restrict exhaust flow through the DPF reducing engine
efficiency. This restriction in exhaust flow produces a
pressure drop across the DPF that increases as the
once porous cell walls become saturated with trapped
soot. The DPS monitors the pressure drop across the
DPF and provides the ECM with a voltage signal
proportional to soot buildup. Once soot buildup reaches
a specified limit (100%), as signaled by the increased
pressure drop across the DPF, the ECM commands a
regeneration event to burn-off the collected soot during
normal vehicle operation. Regeneration events
occurring during vehicle operation are known as normal
regenerations as they occur automatically and without
driver knowledge. In general, the vehicle will need to be
driven safely at a steady speed, preferably without
stopping for approximately 20–30 minutes for a full and
effective regeneration to complete.

Diesel Particulate Filter (Exhaust
Particulate Filter)

Selective Catalyst Reduction (Warm up
Nitrogen Oxides Catalytic Converter)

Diesel Particulate Filter (Exhaust Particulate Filter)
Overview
The DPF captures diesel exhaust gas particulates, also
known as soot, preventing their release into the
atmosphere. This is accomplished by forcing
particulate-laden exhaust through a filter substrate

Selective Catalyst Reduction (Warm up Nitrogen
Oxides Catalytic Converter)
While diesel engines are more fuel efficient and
produce less HC and CO than gasoline engines, they
generate higher levels of Nitrous Oxide (NOx). In order

Bulletin No.: 18-NA-366

November, 2019

to meet today’s tighter NOx limits, an SCR catalyst,
using the injected DEF, is used to convert NOx into N2
and H2O.
NOx Sensor (Nitrogen Oxides Sensor) Operation
The ECM uses two smart NOx sensors to control
exhaust NOx levels. The first NOx sensor is located in
the DOC inlet and monitors the engine out NOx. The
second NOx sensor is located in the exhaust tailpipe
downstream of the SCR and monitors NOx levels
exiting the aftertreatment system. The smart NOx
sensors communicate with the ECM over the serial
data line.
The smart NOx sensors consist of two components, the
NOx module and the NOx sensor element that are
serviced as a unit. The NOx sensors incorporate an
electric heater that is controlled by the NOx module to
quickly bring the sensors to operating temperature. As
moisture remaining in the exhaust pipe could interfere
with sensor operation, there is a delay turning on the
heaters until the exhaust temperature exceeds a
calibrated value. This allows any moisture remaining in
the exhaust pipe to boil off before it can effect NOx
sensor operation. Depending on engine temperature at
start up, the delay can be less than a minute or as long
as two minutes. Typically, NOx sensor 1 will reach
operating temperature faster than NOx sensor 2 as it’s
closer to the engine’s hot exhaust. At idle or low engine
speeds, NOx sensor 2 may require up to 5 minutes to
reach operating temperature. The sensors must be hot
before accurate exhaust NOx readings are available to
the ECM.
Diesel Exhaust Fluid (Reductant) Overview
Diesel Exhaust Fluid (DEF) is a mixture of carefully
blended aqueous urea solution of 32.5% high purity
urea (Pharmaceutical Grade Urea) and 67.5%
deionized water. Within the SCR, exhaust heat
converts the urea into ammonia (NH3) that reacts with
NOx to form nitrogen, CO2, and water vapor. Optimum
NOx reduction occurs at SCR temperatures of more
than 480°F (250°C). At lower temperatures, NH3 and
NOx may react to form Ammonium Nitrate (NH4NO3)
which can lead to temporary deactivation of the SCR
catalyst. To prevent this, the ECM will suspend DEF
injection when the exhaust temperature is less than a
calibrated minimum.
Exhaust Gas Temperature Sensor (Exhaust
Temperature Sensor)
The engine uses Exhaust Gas Temperature (EGT)
management to maintain the SCR catalyst within the
optimum NOx conversion temperature range of
390–750°F (200–400°C). The ECM monitors the EGT
sensors located upstream and within the SCR in order
to determine if the SCR catalyst is within the
temperature range where maximum NOx conversion
occurs.

Page 15

Particulate Matter Sensor (Exhaust
Particulate Matter Sensor)
Particulate Matter Sensor (Exhaust Particulate
Matter Sensor)
The PM sensor determines the amount of particulates
(soot) in the diesel exhaust gas exiting the tailpipe by
monitoring the collection efficiency of the DPF and this
also assists in emission diagnostics. The PM sensor is
similar to the heated oxygen sensor with a ceramic
element but also includes an individually calibrated
control unit. The PM sensor sensing element includes
two comb-shaped inter-digital electrodes, a heater and
a positive temperature coefficient (PTC) resistor for
temperature measurement.
Particulate Matter Sensor (Exhaust Particulate
Matter Sensor) Operation
The operation of the PM sensor is based on the
electrical conductivity characteristic of the soot. As the
exhaust gas flows over the sensing element, soot is
absorbed in the combs between the electrodes,
eventually creating a conductive path. When the path is
formed, it generates a current based on the voltage
being applied to the element. The measurement
process continues until a preset current value is
reached. To avoid misleading readings, the sensor
operates on a “regenerative” principle, which means
the soot is removed by heating up the element to burn
off the carbon, before the measurement phase begins.
The amount of regenerations is based on vehicle
strategy; when the amount of regeneration is reached,
the cumulative current readings are used to determine
the amount of soot concentration in the exhaust gas,
and thus the collection efficiency of the DPF.
The PM sensor is operated in 3 successive modes:
1. Standby mode after power-up to ensure protective
heating. On power-up, the control unit starts the
heating process to avoid condensation of liquids
on the sensing element. Presence of liquid can
cause thermal shock during the heating process,
resulting in damage to the ceramic element.
Regeneration is not initiated until the dew point
temperature has been exceeded.
2. Regeneration mode is conducted before each
measurement to ensure a soot free sensing
element. Before starting measurements, absorbed
soot is burned off the sensing element by heating it
up; this ensures each measurement starts off at
the same condition. Regeneration is conducted for
a pre-determined period of time based on soot
level.
3. Measurement mode is when soot is actively