23-NA-170 Service Bulletin/Repair Instructions

Bulletin No.: 23-NA-170
Service Bulletin
Date: May, 2025
INFORMATION

Subject:
Diagnostic Tips for Seized or Hard to Rotate Engine, Internal Engine or

Transmission Noise Thump, Knock, Rattle and/or Starter Fuse Blown

This bulletin replaces PIP5900. Please discard PIP5900.
Brand:
Model:
Model Year:

from
CT5

Cadillac
Chevrolet
GMC
Escalade Models
to
2022

2021
2025
2023
Corvette
2019
Express
2021
Silverado 1500 (New

Model)
2019
2019
Silverado 1500
2020
2021
2022
6.2L (LT1, (LT4)
2025
6.2L (LT1, LT4,

LT2)

6.6L (L8T)
2022
2023
Silverado 2500HD/

3500HD
2020
Suburban
2021
Tahoe
2021
Savana
2021
2025
Sierra 1500 (New

Model)
2019
2019
Sierra 1500
2020
2021
2022
2022
Sierra 1500 New

(RPO J22, VIN Digit 5

= H/U)
Copyright 2025 General Motors. All Rights Reserved.
6.2L (L87)
2024
Silverado 1500
Sierra 1500 Limited

(RPO J21, VIN Digit 5

= 8/9)
to
Transmission

:
6.2L (LT4)
2019
Silverado 1500 New

(RPO J22, VIN Digit 5

= A/D)
from
Engine:
6.2L (LT4)
Camaro
Silverado 1500 LTD

(RPO J21, VIN Digit 5

= W/Y)
VIN:
4.3L (LV3)

5.3L (L82)

5.3L (L84)

6.2L (L87)
6.6L (L8T)

2025
5.3L (L84)

6.2L (L87)

5.3L (L84)

6.2L (L87)

6.6L (L8T)
4.3L (LV3)

5.3L (L82)

5.3L (L84)

6.2L (L87)
M1L

M1M

M5U

N8X

MF6

MGL

MHO

MHS

MHT

MHU

MHW

MHX

MI2

MI4

MLM

MQB

MQD

MQE

MTH

MYC

MYD
Page 2

Brand:
May, 2025

Model:
Model Year:

from
Sierra 1500
2023
Sierra 2500HD/

3500HD
2020
Yukon Models
2021
Involved Region or Country
Bulletin No.: 23-NA-170
to
2025
VIN:

from
Engine:

to
Transmission

:
6.6L (L8T)

5.3L (L84)

6.2L (L87)
North America, Europe, Kazakhstan, Uzbekistan, Russia, Middle East, Iraq, Israel,

Palestine, Argentina (Mercosur), Brazil (Mercosur), Bolivia (West), Chile (West),

Colombia (West), Ecuador (West), Paraguay (West), Peru (West), Uruguay (West),

Venezuela (West), Other Central America, Japan, Cadillac Korea (South Korea), GM

Korea Company, China - SGM, Taiwan , Thailand (ASEAN), Singapore, Philippines,

Australia/New Zealand, Caribbean, Egypt, Other Africa, South Africa

Some 4.3L, 5.3L, or 6.2L engines may not crank due to being seized with possible starter

fuse being open.

Various engine noises such as but not limited to:

• Thumping (which may be perceived as upper engine noise or possibly from the transmission as shown in the video above.)
Condition
• Growling

• Knocking

• Rattling

Engine may also exhibit a condition of stalling or being hard to rotate once at operating

temperature. Engine could also be locked up and unable to restart. However, upon

engine cooling down to ambient temperature the engine may refire and run normally. This

can be a sign of an early bearing failure.
Cause
This condition may be caused by a crankshaft bearing failure and/or possible damaged

thrust bearing.

Bearings Diagnosis:

If any of the above issues are present and the condition has been identified as an internal

engine concern, the following may be helpful:

Note: If the engine has not had its first oil change it is possible to see some light glitter in

the oil. This could be build debris from the manufacturing process that is flushed out after

the engine has been in operation. Further inspection in this case will be necessary.

- Inspect the engine oil and filter for excessive metal debris, specifically bearing material.

⇒
If bearing debris has been identified, then it will be necessary to remove the engine

oil pan for further inspection of the crankshaft rod and main bearings.

If it has been found there is damage to the crankshaft bearings, please follow the latest

versions of Technical Service Bulletins 22-NA-074 and 18-NA-073 for further repair

direction.
Information
Diagnostic Aids: Stationary Vehicle:

• At a warm idle, increase the engine RPM to 1500 - 1800, and release to see if the

noise intensity increases and decreases

• The use of a stethoscope or Pico scope may show the noise is in the bellhousing or

rear of the transmission.

• Remove the engine oil filter and inspect for metallic and bearing material. Pouring the

engine oil through a white shop towel may be helpful. If material is found perform a

crankshaft end play measurement following published Service Information. Replace or

repair the engine as necessary.

• DO NOT back the torque converter off from the engine and run the engine in an effort

to isolate the noise to the engine or transmission. Many evaluations indicate the noise

is eliminated when the transmission disconnected however replacing the transmission

does not resolve the noise condition. Doing so may also cause engine and or transmission damage.
Bulletin No.: 23-NA-170
May, 2025
Page 3
• If excessive crank end play is not found the engine accessory drive belt should be removed and the engine ran again to see if the noise eliminated. If the noise is eliminated check the accessory drive belt driven components for possible issues.

If it has been found there is damage to the crankshaft bearings, please follow the latest

versions of Technical Service Bulletins 22-NA-074 and 18-NA-073 for further repair

direction.

Starter Concerns:

• If you find it necessary to replace the engine assembly, upon completion of the engine

replacement, ensure that the engine starts and runs as designed and there are no other concerns.

− If the starter fuse is or was blown replace the starter fuse and ensure the vehicle

starts up and operates as designed

• If you noticed that the starter fuse was blown it will be necessary to replace the starter

fuse once new engine is installed. Do not replace the starter assembly. After fuse replacement, if you find that there may be a starter concern refer to diagnostic information in service information for further details.
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.
Version
5
Modified
Released September 19, 2023

Revised September 22, 2023 - Revise Model section and added Additional Countries to

Involved Region or Country section.

Revised January 16, 2024 - Added 2024 Model Year to Applicable Models.

Revised March 11, 2024 - Added Transmission RPO, Update Correction section to add a

video and additional Information, Update Information section to add a Note under Bearing

Diagnosis section, Added Diagnostic Aids: Stationary Vehicle section.

Revised May 15, 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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TECHNICIAN

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