NHTSA ID Number: 10244949
Manufacturer Communication Number: 21-NA-275
TSB/Document Date: 2023-11-06
Summary
This service bulletin provides repair information to correct customer concerns of Rear Wheel Lock Up, ABS Event, Loud Bang and a Flashing “D†on Driver Information Center (DIC) when Lightly or Moderately Accelerating Forcing an 8-7 or 8-6 Downshift.
Bulletin No.:
Service Bulletin
Date:
21-NA-275
October, 2023
TECHNICAL
Subject:
Brand:
Rear Wheel Lock Up, ABS Event, Loud Bang and a Flashing “D” on Driver Information
Center (DIC) when Lightly or Moderately Accelerating, Forcing an 8-7 or 8-6 Downshift
Model:
VIN:
to
Transmission:
(Automatic)
2020
2021
CT6
2019
2021
Escalade Models
2021
2021
LM2
MQC
Silverado 1500
2020
2021
LM2
MQB
Silverado
2500HD/3500HD
2020
2021
L5P
MGM, MGU
Suburban
2021
2021
LM2
MQC
Tahoe
2021
2021
LM2
MQC
Sierra 1500
2020
2021
LM2
MQB
Sierra
2500HD/3500HD
2020
2021
L5P
MGM, MGU
Yukon
2021
2021
LM2
MQC
CT5
from
to
CT4
Cadillac
Model Year:
from
MQA
LSY LGX
MHS
MHS
—
—
Involved Region or Country
North America, Uzbekistan, Russia, Middle East, Israel, Palestine, Bolivia, Chile,
Colombia, Ecuador, Paraguay, Peru, Uruguay, Venezuela, China, Australia, New
Zealand.
Condition
Some customers may comment on the following conditions while lightly to moderately
accelerating, forcing an 8-7 or 8-6 downshift between 64-96 km/h (40-60 mph) with the
transmission at operating temperature:
• Rear wheel/tire lockup or an ABS event
• Loud bang
• Very hard 8-7 or 8-6 downshift
• Feeling of hitting a large pothole or large speed bump
• Flashing “D” on the DIC
Cause
This condition may be caused by an internal control valve body issue.
Correction
Replace the valve body assembly. Refer to Control Valve Body Replacement in SI.
Copyright 2023 General Motors LLC. All Rights Reserved.
Page 2
October, 2023
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.
Parts Information
Use the VIN and refer to the GM Electronic Parts
Catalog (EPC) to determine the proper part to order.
Causal
Part
Description
Part
Number
Qty
VALVE, CONT
(CT4, CT5, CT6)
1
X
VALVE, CONT
(2020 T1 LD)
24044189
1
VALVE, CONT
(Second Design
2020 and 2021
T1 HD)
24044274
X
VALVE, CONT
(First Design 2020
T1 HD)
N/A
Description
Part
Number
19352619
(U.S.A.)
19352620
(Canada)
Transmission
Fluid
24047334
X
VALVE
ASM,- CONT
X
VALVE
ASM,- CONT
24043770
1
X
VALVE
ASM,- CONT
1
N/A
SEAL, A/TRNS
AUX
FLUID PUMP
As Required
For vehicles repaired under the Emission coverage,
use the following labor operation. Reference the
Applicable Warranties section of Investigate Vehicle
History (IVH) for coverage information.
Labor
Operation
Description
Vehicle
CT5
1
1
Qty
Warranty Information
CT4
X
X
Causal
Part
Bulletin No.: 21-NA-275
Labor Time
2.2 hrs
CT6
2.0 hrs
Silverado
1500
3.9 hrs
Sierra 1500
8486158*
Test Drive/
Diagnostic/
Control
Valve Body
Replace
1
Silverado
2500HD/
3500HD
Sierra
2500HD/
3500HD
2.0 hrs
Escalade
Suburban
Tahoe
3.1 hrs
Yukon
24047734
1
*This is a unique Labor Operation for bulletin use only.
Version
4
Modified
Released January 25, 2022
Revised May 19, 2022 – Updated Parts Information section and added Unique Labor
Operation number in Warranty Information section and added more Keywords.
Revised August 23, 2022 – Added an Important statement and updated Transmission
Fluid Quantity in the Parts Information section.
Revised October 10, 2023 - Added LGX to CT4, CT5, and CT6.
Additional SI Keywords: shift, down, brake, braking,
unwanted
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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TSB/Document ID: 21-NA-275
Replacement Service Bulletin Number:
MFR Communication Date: 2023-10-10
MFR Internal Campaign ID/Software Version:
Communication Type: Service Bulletin/Repair Instructions
NHTSA Components: POWER TRAIN
MFR Component System:
MFR Component Subsystem:
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