NHTSA ID Number: 11020259
Manufacturer Communication Number: 21-NA-238
TSB/Document Date: 2025-07-07
Summary
This technical bulletin provides a procedure to inspect the front pump of the transmission for a possible leak.
Bulletin No.: 21-NA-238
Service Bulletin
Date: May, 2025
TECHNICAL
Subject:
Brand:
Transmission Fluid Leak Near Bellhousing Area
Model:
Model Year:
Silverado 2500HD/
3500HD
Sierra 2500HD/
3500HD
from
to
2020
2025
VIN:
from
Engine:
L5P, L8T
MGM, MGU, MKM
to
Involved Region or Country
North America, Australia, New Zealand.
Condition
Some customers may comment that a transmission fluid leak is coming from the
bellhousing inspection cover.
Cause
This condition may be caused by the Automatic Transmission Case Front Cover Seal
may be rolled or damaged.
Correction
If the leak has been verified to be coming from the front cover seal, replace the Automatic
Transmission Case Front Cover Seal and the Torque Converter Fluid Seal.
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.
Service Procedure
Refer to Automatic Transmission Case Front Cover Removal and Torque Converter Fluid Seal Replacement in SI.
Note: Case Front Cover Bolt Specification:
• First Pass: Hand Tighten
• Second Pass: 5 Y (44 lb in)
• Final Pass: 10.5 Y (93 lb in)
Parts Information
Causal
Part
Description
Part
Number
Qty
X
SEAL, T/C FLUID
24293986
1
X
SEAL AUTO
TRANS FRT
CASE COVER
24277112
1
Copyright 2025 General Motors. All Rights Reserved.
Page 2
May, 2025
Causal
Part
Description
Part
Number
Qty
N/A
SEAL, TRANS
FLUID CLR PIPE
85630659
1
N/A
SEAL-EXH SYS
84013962
(L5P)
1
N/A
GASKET-EXH
MANIF PIPE
15126137
(L5P)
2
N/A
SEAL-EXH
MANIF PIPE
(Left)
20987829
(L8T)
1
N/A
SEAL-EXH
MANIF PIPE
(Right)
15077362
(L8T)
1
N/A
BOLT/SCREWFRT PROP SHF
11548472
(4wd)
4
N/A
CLAMP-F/AXL
PROP SHF SLIP
YOKE BOOT
84526283
(4wd)
2
N/A
PLATE, CLU
PRESS
24052451
1
N/A
BOLT/SCREW-A/
TRNS CASE FRT
CVR
11604747
15
N/A
BOLT, TRNS
MNT
11548787
2
N/A
NUT, TRNS MNT
11548414
3
N/A
MOUNT, TRANS
85573625
1
N/A
24286193
1
N/A
FLUID, AUTO
TRNS ULV
19352619
(U.S.)
19352620
(Canada)
15
Bulletin No.: 21-NA-238
Warranty Information
For vehicles repaired under warranty, use:
Labor Operation
Description
Labor Time
8466580
Automatic Transmission Case Front Cover Seal Replacement
Use the Published Labor
Operations Time
Bulletin No.: 21-NA-238
May, 2025
Page 3
Version
9
Modified
Released November 09, 2021
Revised February 17, 2022 - Add 2022 to Model Year.
Revised January 19, 2023 - Added Plate, Clutch Pressure and SEAL, TRANS FLUID
CLR PIPE to Parts Information section.
Revised January 03, 2024 - Added 2023 to 2024 Model Years, Added RPO MKM and
Added 11604747 to Parts Information section.
Revised January 22, 2024 - Added L8T to Engine section, Note to Service Procedure
section and Added New Pipe Seal and Plate Part Numbers.
Revised February 20, 2024 - Added Transmission Mount to Parts Information section.
Revised May 30, 2024 - Added Front Cover Torque Specification to Service Procedure
section.
Revised July 16, 2024 - Added New Parts to Parts Information Section.
Revised May 08, 2025 – Added 2025 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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TSB/Document ID: 21-NA-238
Replacement Service Bulletin Number:
MFR Communication Date: 2025-05-08
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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