Bulletin No.:

Service Bulletin

Date:

16-NA-372
October, 2020

INFORMATION
Subject:

Information on Duramax Diesel 6.6L Common Engine Noises
Model Year:

Brand:

Model:
Silverado

2017

2018

Chevrolet

Silverado 2500/3500

2019

2021

Silverado LD

2019

2019

Sierra

2017

2018

Sierra 2500/3500

2019

2021

Sierra Limited

2019

2019

GMC

from

to

VIN:
from

to

Engine:

Transmission:

L5P

Allison

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
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 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
Copyright 2020 General Motors LLC. All Rights Reserved.

•

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
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

Page 2

October, 2020

Bulletin No.: 16-NA-372

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

7

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.

Additional Keywords: Allison, A1000, LCT1000,
Transmission, Duramax, 6.6L, Tick, MW7, Tick,
Clicking, Noise

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.

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