23-NA-200

Bulletin No.:
Service Bulletin
Date:
23-NA-200
November, 2023
INFORMATION
Subject:
Diagnostic Aid for Misfire Diagnostics Displaying Incorrect Cylinders for Certain OBD
Monitors Reported in Mode 6
Brand:
Model:
Chevrolet
Corvette
Model Year:
VIN:
from
to
from
to
2023
2023
—
—
Involved Region or Country
Engine:
Transmission:
5.5L (LT6)
—
North America, Chile, Europe, Russia, Middle East, Israel, Palestine, Japan, GM Korea
Company, Thailand, Australia/New Zealand
Note: This issue only affects vehicles with the following ECM software part numbers:
12734308 and 12734747.
Condition
Technicians may find when using a generic scan tool to look at “Fuel System Monitor”
(AFIM – Air fuel Imbalance Monitor) or the “Misfire Cylinder Data”, the scan tool displays
the incorrect cylinder that is impacted.
Cause
SAE J1979 Mode 06 On-board System test results for cylinder specific OBD Monitors are
assigned to the wrong cylinders. The following monitors are impacted:
• Fuel System Monitor (AFIM - Air fuel Imbalance)
• Misfire Monitor
This only impacts vehicles with the following ECM SW part numbers:
• 12734308
• 12734747
Information
Technicians are advised to rely on DTCs for correct cylinder identification when fuel
system monitoring or misfire faults are present.
If the vehicle contains an ECM SW part number that is listed above, the following Cylinder
Decoder table can be used to correct the cylinder assignments which are reported in
mode 06.
Copyright 2023 General Motors LLC. All Rights Reserved.
Page 2
November, 2023
Bulletin No.: 23-NA-200
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.
Additional Information
Cylinder Decoder:
Corrected Cylinder
Assignment
Cylinder Assignment
reported in Mode 06
1
1
2
2
3
4
4
5
5
7
6
8
7
6
8
3
Cylinders 1 and 2 are reported correctly in mode 06 and are
not impacted by this issue.
Version
1
Modified
Released November 06, 2023
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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