19NA233

Bulletin No.:
Service Bulletin
Date:
19-NA-233
January, 2022
INFORMATION
Subject:
Brand:
Chevrolet
GMC
Diagnostic Tip for Misfire, Malfunction Indicator Lamp (MIL) Illuminated - DTCs P0300,
P0301, P0302, P0303 and/or P0304
Model:
Model Year:
from
Colorado
2016
Express
2017
Canyon
2016
Savana
2017
to
2022
VIN:
from
to
Engine:
Transmission:
LWN
Involved Region or Country
North America
Condition
Some customers may comment on one or more of the following conditions:
• MIL illuminated
• Misfire
Some technicians may find one or more of the following DTCs set in the Engine Control
Module (ECM):
• P0300
• P0301
• P0302
• P0303
• P0304
Cause
This condition may be caused by one or more of the following conditions:
• Fuel Injector
• Electrical issue
• Loss of cylinder compression
Correction
Note: The purpose of this bulletin is to show you a way to confirm if you have a
mechanical engine issue or not.
A Relative Compression test can be used to determine if the misfire is caused by an
engine compression issue or not.
Service Procedure for Running a
Compression Test
A technician may find that a relative compression test
can be used to rule out an engine compression issue. A
relative compression test can be performed with
different tools and the engine can be cranked over
using many different methods.
For this communication, use the PicoScope CH-51450
and available CH-51450-LEAD kits or equivalent.
Copyright 2022 General Motors LLC. All Rights Reserved.
Note: Pull the Fuel Pump Relay so the engine can be
cranked without any fuel being delivered to the engine.
1. Remove the Fuel Pump Relay from the Underhood
Fuse Block.
2. Connect the PicoScope to the computer using the
included USB cable as you would do using
GM NVH.
3. Connect test leads to the battery (hook the colored
lead to Battery (+) and the black lead to Battery (-))
and to channel A of the PicoScope.
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Bulletin No.: 19-NA-233
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4. Open the most current version of PicoScope 6
Automotive for GM software that is loaded when
GM NVH software is installed.
⇒ If Picoscope 6 Automotive is not on your
computer, download the newest version of Pico
Scope NVH Software Update
V.R.1.11.1_September_2018 or later.
5419699
5. With the PioScope hooked up and the software
running, a steady line at battery voltage on the
graph should be displayed.
Bulletin No.: 19-NA-233
January, 2022
Page 3
5419709
6. Select the Collection Time drop down.
5419718
7. Change the collection time from 5ms/div to 200
ms/div.
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8. Crank the engine for two to three seconds.
9. Immediately after cranking the engine, select the
Stop capturing button at the bottom of the screen.
5419733
10. Save this file to the PC.
⇒ It may be useful to repeat steps 8 thru 10 a few
more times to collect additional wave forms. To
do this, you will need to hit the Go or Start
capturing button prior to cranking the engine.
11. Disconnect the PicoScope.
12. Reinstall the Fuel Pump relay.
13. If any codes have set as a result of removing the
fuel pump relay, clear them.
Bulletin No.: 19-NA-233
January, 2022
Page 5
Setting Up PicoScope 6 Software to
View Waveforms
5419752
To examine one of these wave forms, use the
Waveform Buffer Index navigation buttons to locate the
start of the cranking.
5419756
To view the Wave Form, zoom in to the right side of the
graph.
The graphic above depicts a viewable Wave Form
Pattern.
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Change settings.
⇒ Select the drop down next to the blue “A” (for
channel A).
5419767
The channel options screen should be displayed.
⇒ Select the Lowpass Filtering Active Filtering check
box (1kHz to start).
⇒ Change the Axis Scaling Scale value to 26.00.
Bulletin No.: 19-NA-233
January, 2022
Page 7
5419779
Take note, the voltage graph appears to have
disappeared, but if you look at the scaling on the left,
you will see that the value is a very high negative
number.
⇒ Use the axis scaling offset to bring the graph back
into view.
5419787
The graphic above depicts a viewable Voltage Graph
Pattern.
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Bulletin No.: 19-NA-233
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Use the waveform Buffer button to move to the next
window.
5419821
The graph above illustrates an engine that will pass a
compression test and there is no reason to think that
there is anything mechanically wrong with the engine.
⇒ If the graph does not look like the graph above,
Refer to Analyzing Relative Compression Graphs
section below.
Bulletin No.: 19-NA-233
January, 2022
Page 9
Analyzing Relative Compression
Graphs
5419916
When examining these graphs, view the downward
portion of the waveform.
This area of the graph is the engine starter pulling more
electricity from the battery during a compression stroke.
5419910
Utilizing a horizontal ruler, line up the bottom of the
waveform.
⇒ Select the blue box and drag it to the location that's
viewable.
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Bulletin No.: 19-NA-233
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Vertical rulers may be used as well.
5419944
Utilize a second ruler.
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January, 2022
Page 11
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Select the Ruler Settings Button to display the Ruler
Setting menu options.
5419955
Change the rotation partition to 4, to represent the
number of cylinders in the engine.
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This should help to identify the top of each compression
stroke in two rotations of the engine.
It is not an issue if you see a few of these “tips” that do
not touch the line. What we are looking for is
consistently one of every four points not hitting the line
for a four cylinder engine.
Sample Waveforms for Reference
5420017
The graphic above depicts an example of an
eight-cylinder engine with a cylinder that has no
compression in one cylinder.
Note that one of the dips is missing and it repeats every
eight dips.
– This is a clear indication that there is an issue with
this engine.
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January, 2022
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5420027
The graphic above depicts an example of a
four-cylinder engine with a bad exhaust cam lobe.
Note that consistently there is one cylinder with an
extra-long compression stroke.
– Examination of this engine showed that cylinder
number four had a worn down cam lobe.
5420028
This is a four-cylinder engine with a 20 PSI loss in one
cylinder
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This is a four-cylinder engine with a 40 PSI loss in one
cylinder.
5420040
This is a four-cylinder engine with a 60 PSI loss in one
cylinder.
Bulletin No.: 19-NA-233
January, 2022
Page 15
5420048
If an engine has low or high compression on one
cylinder, it may be useful to add an injector pulse or a
Camshaft Position Sensor to help determine which
cylinder has an issue.
The graphic above shows the signal from the Cam
Position Sensor for reference.
Background Information
By graphing the battery voltage while cranking an
engine we can get a good picture of how the
compression in each cylinder compares to the
compression in each other cylinders in the engine.
When you think about an engine being cranked over by
the starter, each time a piston compresses the charge
in the cylinder, the drag on the starter increases which
in turn increases the starter draw and decreases the
battery voltage until the air in the cylinder is
compressed.
After this compression stroke and before the next
cylinder in the firing order begins its compression
stroke, there is a short period of cranking where the
voltage increases. This is what gives the us the pattern
to examine on a scope as well as the distinctive sound
of an engine being cranked.
If each cylinder in the engine are of very close
compression, the resulting pattern on the scope will be
equal all the way across the screen. If one of the
cylinders in a four-cylinder engine has low compression
compared to the other three, then every four “waves”
will look different than the other three. The same can be
said of an eight-cylinder engine that has a weak
cylinder, the wave pattern will look different on every
eighth wave.
Version
3
Modified
Released October 14, 2019
Revised October 20, 2020 – Added 2021 Model Years
Revised January 10, 2022 – Added 2022 Model Years
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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