Reductant Control Module, CAN
Interface
DEF Pressure Sensor
DEF Heaters — to Reductant Control
Module
DEF Pump — to Reductant Control
Module
DEF Continuous Level Sensor — to
Reductant Control Module
DEF Temperature Sensor — to
Reductant Control Module

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 (PM) in the engine exhaust gases.
Reducing these pollutants to acceptable levels is
achieved using the following components:
1. Close Coupled Diesel Oxidation Catalyst
(DOC): The close coupled DOC functions similar
to the catalytic converter used with gasoline
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. Proper
DOC function requires the use of ultra-low sulfur
diesel (ULSD) fuel containing less than 15 ppm
sulfur.
2. Selective Catalyst Reduction (SCR): Diesel
engines are more fuel efficient and produce less
HC and CO than gasoline engines, however they
generate much higher levels of NOx. In order to

(8)
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(11)
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(13)
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(15)
(16)
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DEF Quality Sensor — to Reductant
Control Module
Exhaust Gas Temperature Sensor [5x]
HC Injector
DPF Differential Pressure Sensor
PM Sensor, CAN Interface
DPF
DOC
NOx Sensor [2x] — CAN Interface
SCR
DEF Injector
Close Coupled DOC

meet the current NOx limits, an SCR catalyst,
along with reductant, is used to convert NOx into
N2, CO2, and H2O.
3. Diesel Oxidation Catalyst (DOC): In addition to
reducing emissions, the DOC also generates the
exhaust heat needed by the SCR to properly
function. Exhaust gas temperature sensors are
located upstream and downstream of the DOC. By
monitoring the temperature differential between
these 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 diesel fuel into the
exhaust gases entering the DOC. This is
accomplished by means of a hydrocarbon injector
(HCI) upstream of the DOC in the exhaust system.

Bulletin No.: 19-NA-091

June, 2019

4. Diesel Particulate Filter (DPF): 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
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
(PM). The DPF is capable of removing more than
90% of particulate matter, or soot carried in the
exhaust gases.
DEF
Depending on the information being referenced,
reductant is also identified as diesel exhaust fluid (DEF)
which is a mixture of specifically 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.
DEF Heaters for Cold Weather Operation
A 32.5% solution of urea with 67.5% deionized water
will begin to crystallize and freeze at 12°F (−11°C). At
this ratio, both the urea and water will freeze at the
same rate, ensuring that as it thaws, the fluid does not
become diluted, or over concentrated. The freezing and
thawing of DEF will not cause degradation of the
product. There are two DEF heaters in the system. DEF
Heater 1 is in the DEF reservoir and DEF Heater 2 is in
the supply line to the DEF injector. The K115 Reductant
Control Module monitors the B214 Reductant
Temperature Sensor located within the reservoir in
order to determine if the DEF temperature is below its
freeze point. If the module determines that the DEF
may be frozen, it energizes the DEF heaters. DEF
pump operation is disabled for a calibrated amount of
time to allow the heaters an adequate amount of time to
thaw the frozen DEF. Once the thaw time period
expires, the module energizes the DEF pump to
circulate warm DEF back to the reservoir to speed
thawing. The ECM looks for an increase in the DEF
temperature to verify that the DEF reservoir heater is
working.
DEF Injector
The ECM energizes the DEF injector in order to
dispense a precise amount of reductant upstream of
the SCR in response to changes in exhaust NOx levels.
The signal from NOx Sensors 1 and 2 allow the ECM to
accurately control the amount of DEF supplied to the
SCR. If more DEF is supplied to the SCR than is
needed for a given NOx level, the excess DEF results
in what is called ammonia slip where significant levels
of ammonia exit the SCR. Since the NOx sensors are

Page 13

unable to differentiate between NOx and ammonia, the
ammonia slip will cause NOx Sensor 2 to detect higher
NOx levels than actually exist.
DEF Level
The DEF level must be maintained for the vehicle to run
properly. As the DEF level becomes low, warnings are
displayed on the DIC. These warnings will increase in
intensity as the DEF level is reduced. As the tank nears
empty, vehicle speed will be limited in a series of steps.
At least 2 gallons (7.57 L) of DEF must be added to
release the speed limitation.
DEF Reservoir Components
The DEF system reservoir components consist of the
following: :
• An electrically-operated DEF pump
• An integrated B213A Reductant Level Sensor 1
and B214 Reductant Temperature Sensor
• K115 Reductant Control Module
• B295 Reductant Quality Sensor
• Reductant system heaters
• An electrically controlled DEF injector which is
external to the reservoir.
Exhaust Gas Temperature (EGT) Sensor
The engine uses exhaust gas temperature
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 downstream of the SCR
in order to determine if the SCR catalyst is within the
temperature range where maximum NOx conversion
occurs.
NOx Sensor
The ECM uses two smart NOx sensors to monitor the
exhaust NOx levels. The first NOx sensor is located at
the turbocharger outlet and monitors the engine out
NOx. The second NOx sensor is located in the exhaust
pipe 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.
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 to
aid in OBD-II 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.
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

Page 14

June, 2019

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, where the soot
is cleaned off by heating up the element to burn off the
carbon, before the measurement phase begins. The
amount of regenerations is based on vehicle strategy.
The cumulative PM sensor current readings are used to
determine the amount of soot concentration in the
exhaust gas, and determine the collection efficiency of
the DPF and if a regeneration is needed.
Regeneration Process
A number of engine and exhaust aftertreatment
components are required to function together to
perform the regeneration process. The engine
components are the fuel injectors, turbocharger, Intake
Air (IA) valve, fuel pressure control, and the intake air
heater (IAH).

DEF Recommendation — Storage and
Transfer
DEF Recommendation

Bulletin No.: 19-NA-091

API Certified Diesel Exhaust Fluid Logo
• General Motors DEF is an aldehyde free, NOx
reducing treatment. It is a mixture of 32.5% high
purity synthetic urea and 67.5% deionized water.
GM DEF meets the stringent ISO 22241 standard
for purity and concentration. GM DEF is a stable,
colorless, non-flammable, non-toxic primary
component used to help convert NOx, an
environmental pollutant, into harmless nitrogen
and water. Use Diesel Exhaust Fluid
GM PN 19286291, in Canada 88862660 or DEF
that meets the International Organization for
Standardization ISO 22241 specification or
displays the API Certified Diesel Exhaust Fluid
Mark (meets API certification requirements).
Classified as minimum risk for transportation.
• ACDelco® DEF is an aldehyde free, NOx reducing
treatment. It is a mixture of 32.5% high purity
synthetic urea and 67.5% deionized water.
ACDelco® DEF meets the stringent ISO 22241
standard for purity and concentration. ACDelco®
DEF is a stable, colorless, non-flammable,
non-toxic primary component used to help convert
NOx, an environmental pollutant, into harmless
nitrogen and water. It meets API regulations, and
meets or exceeds GM OE specifications.
Classified as minimum risk for transportation.
Storage and Transfer
DEF has a shelf life of approximately 24 months, but
when exposed to sunlight or prolonged exposure to
temperatures warmer than 75°F (23.8°C), the nitrogen
in DEF begins to volatilize into ammonia gas and can
reduce shelf life. Once volatilized, it will not go back into
suspension and the percentage of urea in the product
decreases to less than the optimum 32.5%. Fresh DEF
has a slightly pungent smell of ammonia. After
extended exposure to temperatures warmer than 75°F
(23.8°C), the ammonia scent grows stronger, indicating
nitrogen has vaporized, changing the urea-to-water
ratio of the product. Because DEF is highly reactive to
many metals, it must be stored in stainless steel,
polypropylene or high-density polyethylene (HDPE)
storage tanks. All pumps, valves and fittings must be
DEF compatible and used only to transfer DEF.

5138259

Bulletin No.: 19-NA-091

June, 2019

Warning Light

Page 15

Specification

5152580

5123610

When there is an issue with the DEF such as a low fluid
level or fluid contamination, the DEF Warning Light will
illuminate, a DIC message will display and a chime will
sound. To avoid vehicle speed limitations, fill the DEF
tank at the first opportunity after a Low Fluid Level
warning message displays.

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.

Engine Oil — 6.6L Diesel

Viscosity Grade
Use SAE 15W-40 viscosity grade engine oil. In an area
of extreme cold, where the temperature is colder than
0°F (−18°C), use SAE 5W-40. An oil of this viscosity
grade will provide easier cold starting for the engine at
extremely cold temperatures.

Ash Loading
Ash is a non-combustible by-product occurring from
normal oil consumption. Low ash content engine oil
(CJ-4 or CK-4) is required for these diesel engine
equipped vehicles because of the exhaust
aftertreatment system. Ash accumulation will eventually
cause a restriction in the DPF. Being non-combustible,
ash is not burned off during regeneration. A DPF that is
ash loaded will need to be replaced.

Head-Up Display

5323981

Both vehicles offer an available multicolor 15-inch
(381 mm) diagonal Head-Up Display (HUD) to help
keep the driver’s eyes on the road by conveniently

Page 16

June, 2019

projecting key information directly onto the windshield
such as speed, active safety information, available
Navigation and an inclinometer that measures grade.

Supplemental Inflatable Restraint
System
Overview
The supplemental inflatable restraint (SIR) system
supplements the protection offered by the seat belts.
The SIR system contains an Inflatable Restraint
Sensing and Diagnostic Module (SDM), air bags, seat
belt pretensioner (anchor and retractor), and impact
sensors. The SDM is a microprocessor and the control
center for the SIR system. The SDM determines the
severity of a collision with the assistance of impact
sensors located at strategic points on the vehicle.
When the SDM detects a collision, it will process the
information provided by the sensors to further support
air bag or pretensioner deployment. The SDM will
deploy the air bags and pretensioners if it detects a
collision of sufficient force. If the force of the impact is
not sufficient to warrant air bag deployment, the SDM
may still deploy the seat belt pretensioners. The SDM
contains a sensing device that converts vehicle velocity
changes to an electrical signal. The SDM compares
these signals to calibrated values stored in its memory.
If the signals exceed a calibrated value, the SDM will
determine the severity of the impact and either cause
current to flow through the frontal deployment loops
deploying the frontal air bags and pretensioners, or it
will deploy the pretensioners only. The SDM
continuously monitors the deployment loops and the
SIR system electrical components for malfunctions and
illuminates the SIR system AIR BAG indicator if a fault
is detected.
Air Bags
These vehicles contain 7 air bags. The 7 air bags are
located in the steering wheel (dual air bags), instrument
panel (passenger side) (dual air bags), driver side seat
inboard side, driver side seat outboard side, passenger
side (seat), left roof rail, right roof rail. Air bags contain
a housing, inflatable air bag, two initiating devices (if
dual air bags), a canister of gas generating material
and, in some cases, stored compressed gas. The
deployment loops supply current to deploy the air bags.
The steering wheel and passenger instrument panel air
bags have two stages of deployment, which varies the
amount of restraint to the occupant according to the
collision severity. For moderate frontal collisions the air
bags deploy at less than full deployment which consists
of stage 1. For more severe frontal collisions a full
deployment is initiated which consists of stage 1 and
stage 2. The current passing through the air bags ignite
the material in the canister producing a rapid
generation of gas and is some cases, the release of
compressed gas. The gas produced from this reaction
rapidly inflates the air bag. Once the air bag is inflated it
quickly deflates through the air bag vent holes and/or
the bag fabric. A shorting bar (if equipped) is located in
the air bag connector.

Bulletin No.: 19-NA-091

Impact Sensors
There are multiple impact sensors which may be
located in the front of the vehicle, in the front doors or
on the B-pillar, and on the C-pillar depending on the
vehicle configuration. The front of vehicle, B-pillar, and
C-pillar impact sensors contain a sensing device which
monitors vehicle acceleration to detect collisions that
are severe enough to warrant air bag deployment. The
front door impact sensors contain a sensing device
which monitors the door cavity air pressure change to
detect side collisions that are severe enough to warrant
air bag deployment. It is important when working on
components in the door to make sure any items which
have a sealing impact on the door (water deflector,
exterior door handle, speaker, door harness grommet,
or sealing strip) are securely fastened when reinstalled.
The impact sensors are not part of the deployment
loop, but instead provide input to the SDM.
Seat Belt Pretensioners
Important: Once a pyrotechnic pretensioner is
activated it must be replaced.
The pyrotechnic pretensioner is the most sophisticated
type of pretensioning device. The seat belt pretensioner
(driver and passenger) consist of a housing, seat belt
retractor (located in the B-pillar), seat belt anchor
(located in the seat), seat belt webbing, an initiator, and
a canister of gas generating materials. The initiator is
part of the seat belt pretensioner deployment loop.
When the vehicle is involved in a collision of sufficient
force, the SDM causes current to flow through the seat
belt deployment loops to the initiator. Current passing
through the initiator ignites the material in the canister
producing a rapid generation of gas. The gas produced
from this reaction deploys the seat belt pretensioners
which removes all of the slack in the seat belts.
Depending on the severity of the collision, the seat belt
pretensioners may deploy without the frontal air bags
deploying, or they will deploy immediately before the
frontal air bags deploy. A shorting bar (if equipped) is
located in the connector.
Snow Plow
The air bag system was designed to work properly
under a wide range of conditions, including snow
plowing with vehicles that have the optional snow plow
prep package — RPO VYU
DO NOT change or defeat the snow plow's "tripping
mechanism" because it can damage the snow plow and
the vehicle, and may cause an air bag deployment.

Suspension — Front
Short long arms independent front suspension with
torsion bars.

Suspension — Rear
Semi-elliptic three-stage multi-leaf spring.

Bulletin No.: 19-NA-091

June, 2019

Tire Rotation — Tire and Loading
Information Label

Page 17

Tire Rotation Pattern — Polished Forged Dual
Aluminum Wheels

Tire and Loading Information Label
A vehicle-specific Tire and Loading Information label is
attached to the center pillar (B-pillar). The Tire and
Loading Information label shows the number of
occupant seating positions, and the maximum vehicle
capacity weight in pounds and kilograms. The Tire and
Loading Information label also shows the size of the
original equipment tires and the recommended cold tire
inflation pressures. There is also important loading
information on the vehicle Certification/Tire label. It may
show the Gross Vehicle Weight Rating (GVWR) and the
Gross Axle Weight Rating (GAWR) for the front and
rear axles.
Tire Rotation
Tires should be rotated every 7,500 mi (12,000 km).
Tires are rotated to achieve a uniform wear for all tires.
The first rotation is the most important. The outer tire on
a dual wheel setup generally wears faster than the
inner tire. Adjust the front and rear tires to the
recommended inflation pressure on the Tire and
Loading Information label after the tires have been
rotated.
Tire Rotation Pattern — Single Rear Wheels

5152010

Vehicles with polished forged aluminum dual wheels
have three unique wheels; a front, a rear outer and a
rear inner. These wheels cannot be rotated to another
position, however, they can be rotated from left to right
to the same position.
Use this rotation pattern when rotating the tires if the
vehicle has polished forged aluminum dual rear wheels.
The spare wheel can be used in any position in the
event of a flat tire, and can be rotated with the rear
inner wheels. After the flat tire is repaired, if the spare is
not on one of the inner rear positions, it must be
replaced by the correct wheel in the front or rear outer
positions.
Tire Rotation Pattern — Dual Rear Wheels

5318508

Use this rotation pattern when rotating the tires if the
vehicle has single rear wheels.

5151982

Use this rotation pattern when rotating the tires if the
vehicle has dual rear wheels (except polished forged
aluminum wheels).

Page 18

June, 2019

Trailer Detection
With RPO U1D
The K68 Trailer Lighting Control Module is supplied
with battery voltage as well as ignition voltage and is
permanently grounded. The trailer lighting control
module constantly monitors for trailer connection
status, this is accomplished through the lighting circuits
of the trailer to determine if a trailer is connected. With
the key OFF, the K68 Trailer Lighting Control Module
will periodically pulse the lighting circuits of the trailer to
verify it is still connected. Depending on the
configuration of the trailer lights, the trailer lights may
periodically flash as part of the trailer theft deterrent
function. These flashes correspond to when the K68
Trailer Lighting Control Module pulses the lighting
circuits to ensure the trailer is still connected and is
considered normal. When a trailer is connected, the
K68 Trailer Lighting Control Module senses the trailer
connection and alerts the driver by requesting a trailer
profile setup through the Trailering App, which is
displayed on infotainment screen (P17 Info Display
Module). If a trailer is disconnected with the ignition
ON, the vehicle will display multiple trailer lighting
message faults until a trailer is reconnected or the
ignition is cycled.

Trailering Mirrors

Bulletin No.: 19-NA-091

Extending

5326383

If equipped, grasp the mirror housing firmly and pull
back in one motion, arching slightly toward the rear of
the vehicle.
Retracting

Overview
The trailering mirrors have been redesigned with
improved perimeter lighting. New, larger and more
functional door-mounted trailering mirrors are standard
on all 2500HD and 3500HD models. The mirrors extend
and retract using a four-bar-link system that makes for
smooth operation, whether done with power or
manually. The surface area of the mirrors is larger, for a
greater field of view compared to the current model,
and an available power extension feature makes it
easier to adjust the view from the driving position. New
for 2020 is the forward-facing spot lamp on each mirror
that shines light at about a 45-degree angle, providing
illumination on the job site or camp site. There also are
side-view cameras mounted within the mirror housings,
and when equipped, mirror-mounted puddle lamps and
two rearward-facing spot lamps are also available.

5326390

To return the mirror to its original position, reverse the
motion.
Power Extending Mirrors
If equipped, press the power extend button to fully
extend the mirror. Press it again to retract.