Bulletin No.: 16-NA-372

Service Bulletin

Date: August, 2024

INFORMATION
Subject:

Information on Duramax Diesel 6.6L Common Engine Noises

Brand:

Chevrolet

Model:

Model Year:
from

to

Silverado

2017

2018

Silverado 2500/3500

2019

2025

Silverado 4500HD,
5500HD and 6500HD

2019

2025

Silverado LD

2019

2019

Sierra

2017

2018

Sierra 2500/3500

2019

2025

Sierra Limited

2019

2019

GMC

VIN:
from

Engine:

Transmission:

to
L5P
L5D
MW7, MGM, MGU.
L5P

Involved Region or Country

North America, Middle East, Israel, Palestine: Export Dealers should contact your Local
Technical Assistance Center if there are additional questions.

Condition

A customer may comment on the engine making various noises and may request clarification of what is causing the noise. The noises may be described as a tick, click, or
cycling noise.

Cause

These noises may be coming from various engine components such as the fuel injectors,
intake air flow valve, the turbocharger or the diesel exhaust fluid (DEF) injector and may
be heard when the engine is running or after it has been turned OFF.

Correction

Review the Information.

Information
Important: Service agents must comply with all
International, Federal, State, Provincial, and/or
Local laws applicable to the activities it performs
under this bulletin, including but not limited to
handling, deploying, preparing, classifying,
packaging, marking, labeling, and shipping
dangerous goods. In the event of a conflict
between the procedures set forth in this bulletin
and the laws that apply to your dealership, you
must follow those applicable laws.
Tip: United States: A description of these noises
and an audio file of what they sound like can be
found in: 2018 SKH Seminar Feb Emerging Issues
#10218.02V. Canada: Dealers can review TAC Talk

Copyright 2024 General Motors. All Rights Reserved.

52018.03D-0D March 2018 — Powertrain segment.
Advance to timestamp 21:40 to view.
The following information describes these noises:
• Rhythmic Ticking: This is a rhythmic ticking that
can be heard during deceleration. The noise is
usually, but not limited to, heard coming from
around the passenger side of the vehicle. The
noise is from the fuel injectors firing (one injector
per deceleration and not always the same injector)
and is a normal function of the engine and
calibration system.
• Parts Cycling Closed and Open: Some noises
may be coming from under the hood after the
engine has been turned OFF. You may notice that
they are the same noises almost every time the
engine is turned OFF. These noises seem to be

Page 2

August, 2024

coming from the turbocharger and/or the intake
airlow valve. The intake airflow valve is a throttle
plate actuator and is used to achieve high exhaust
gas recirculation rates. These parts will cycle
through their complete normal operating ranges
after the engine is turned OFF. This is a normal
operating condition.
• Diesel Engine Tick: Diesel engine tick is
present in all diesel engines produced in the last
20 years and does not have any impact on engine
reliability and durability. It may be more noticeable
on the 6.6L L5P because of the major reduction in
combustion background noise. This occurs at idle
and may seem to be louder when standing just
behind the driver’s front wheel. The noise may be
more noticeable in the first 20% of engine oil life.
Dealers should not attempt to compare any
customer vehicles exhibiting this noise with other

Bulletin No.: 16-NA-372

similar vehicles as the noise is different from
vehicle to vehicle and this may lead to the incorrect
conclusion that the vehicle has a condition. The
noise is a normal operating characteristic and has
no short or long term effects on the engine. DO
NOT attempt repairs for this noise.
• DEF Injector Noise: A tick noise may be heard
coming from under the vehicle and typically it is
heard at low vehicle speed and especially next to a
building, such as when going through a drive
through. The noise is from the DEF Injector and is
considered a normal operating condition.
The information found in this bulletin can be shared
with customers that may inquire about this condition. In
the event they have additional questions or concerns,
please advise them to contact Customer Assistance.

Version

12

Modified

Released November 14, 2016
Revised August 29, 2017 — Updated Model Years.
Revised September 13, 2017 — Updated Condition.
Revised March 09, 2018 — Updated Information and Condition.
Revised July 23, 2018 - Added the 2019 Model Year.
Revised October 01, 2019 — Added 2020 Model Year, revised the Subject, Condition,
Cause and Correction and clarified the text in the Information section.
Revised October 23, 2020 - Added the 2021 Model Year.
Revised January 06, 2022 - Added Silverado 4500HD, 5500HD and 6500HD to Model
and 2022 to Model Year.
Revised May 25, 2022 - Add Transmission RPOs to Transmission section.
Revised September 07, 2022 - Added the 2023 Model Year.
Revised March 16, 2023 — Added the 2024 Model Year.
Revised August 09, 2025 - Added the 2025 Model Year.

Additional Keywords: Allison, A1000, LCT1000, Transmission, Duramax, 6.6L, Tick, MW7, Tick, Clicking,
Noise, 10 Speed, 10L1000, MGM, MGU

GM bulletins are intended for use by professional technicians, NOT a "do-it-yourselfer". They are written to inform these
technicians of conditions that may occur on some vehicles, or to provide information that could assist in the proper
service of a vehicle. Properly trained technicians have the equipment, tools, safety instructions, and know-how to do a job
properly and safely. If a condition is described, DO NOT assume that the bulletin applies to your vehicle, or that your
vehicle will have that condition. See your GM dealer for information on whether your vehicle may benefit from the
information.

WE SUPPORT VOLUNTARY
TECHNICIAN
CERTIFICATION