19NA187

Bulletin No.:
Service Bulletin
Date:
19-NA-187
January, 2022
INFORMATION
Subject:
Brand:
Chevrolet
GMC
Diagnostic Tip to Identify Engine Misfiring and/or Malfunction Indicator Lamp (MIL)
Illuminated - DTC P0300 Setting
Model:
Model Year:
from
to
Silverado
2017
2018
Silverado 2500/3500
2019
2022
Silverado 4500/
5500/6500
2019
2022
Sierra
2017
2018
Sierra 2500/3500
2019
2022
VIN:
from
to
Engine:
Transmission:
L5P
L5D
L5P
Involved Region or Country
North America and Israel
Condition
Some customers may comment on one or more of the following conditions:
• MIL illuminated
• Engine misfire
Some technicians may find DTC P0300 set in the Engine Control Module (ECM).
Cause
This condition may be caused by a weak cylinder.
Correction
Refer to the Service Procedure below to help identify which cylinder is misfiring.
Copyright 2022 General Motors LLC. All Rights Reserved.
Page 2
January, 2022
Bulletin No.: 19-NA-187
Service Procedure
If there is any difficulty identifying a misfiring cylinder, it
may be useful to graph the Cylinder Balance Test in
GDS2. Do Not rely on this test as the ONLY means of
identifying a weak cylinder.
The balance test should only run when the misfire is
present in the engine. Graph the engine RPM as well
as each injector command. It is recommended to
perform the test a minimum of three times with three
different balance tests while looking for the consistency.
The example below is from an engine that has a misfire
on cylinder #1. It is recommend when setting up the
graph, use the following settings:
5394634
The most important thing is that the RPM line is visible
and not covered by the injector command lines. All
three graphs below, each injector was cancelled in
order, 1 – 8.
5394706
Bulletin No.: 19-NA-187
January, 2022
Page 3
Note that cylinder #1 does not drop the RPM when
canceled, when compared to the other cylinders.
⇒ RPM recovery is limited after the cancellation has
ended.
⇒ Other cylinders do not have as much of a RPM drop
when they are canceled, however the RPM does
jump after the cancellation has ended.
5394746
During this second balance test, it appears like cylinder
#1 is contributing, however it is less than any of the
other cylinders.
5394869
During this final test, it appears that cylinder #5 is not
contributing as well as #1. This is one of the main
reasons that we must repeat the test to find
consistency.
⇒ This vehicle was repaired by replacing #1 fuel
injector.
Note: This is not the only tool that should be used to
identify a misfiring cylinder, but it can help aid in
diagnosing this concern.
Page 4
January, 2022
Bulletin No.: 19-NA-187
Parts Information
No parts are required for this repair.
Version
3
Modified
Released August 23, 2019
Revised October 28, 2020 - Added 2021 Model Year.
Revised January 12, 2022 - Added 2022 Model Year.
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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