24-NA-264 Service Bulletin/Repair Instructions

Bulletin No.: 24-NA-264
Service Bulletin
Date: November, 2024
INFORMATION

Subject:

Brand:
Diagnostic Tips for 10L60/80/90 Transmission Noise

Model:
Model Year:

from
to
2020
2025
Camaro
2020
2025
Silverado 1500
2020
2021
2022
2022
VIN:

from
Engine:
Transmission:
to
CT4

Cadillac
CT5

Escalade Models
Silverado 1500 - LTD

(RPO J21, VIN Digit

5 = W/Y)

Chevrolet
Silverado 1500 New (RPO J22, VIN

Digit 5 = A/D)

Silverado 1500
2023
2025
2020
2025
2020
2021
2022
2022
Sierra 1500
2023
2025
Yukon Models
2020
2025
Suburban

Tahoe

Sierra 1500

Sierra 1500 - Limited

(RPO J21, VIN Digit

5 = 8/9)

GMC
Sierra 1500 - New

(RPO J22, VIN Digit

5 = H/U)
M6F, ML1, ML2,

ML4, MHO, MHS,

MHT, MHU, MHW,

MHX, MQA, MQB,

MQC,
Involved Region or Country
United States, Canada, Middle East, Israel, Palestine, Australia/New Zealand
Condition
Some customers may comment on whine noises from the automatic transmission.
Information
To aid in transmission diagnosing, refer to the noise examples below.
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.
Copyright 2024 General Motors. All Rights Reserved.
Page 2
November, 2024
Bulletin No.: 24-NA-264
Potential Noises Found in Park

Engine Off/Park- Transmission Auxiliary Pump Prime

•10LXX Transmissions equipped with auto start/stop contain an electronic G5 transmission fluid pump. Purpose is to

maintain transmission fluid pressure during auto start/stop events.

•When ambient background level is low (i.e., garage), customers may hear the auxiliary pump cycling for 20 seconds

as they approach the vehicle (Cadillac) or unlock the vehicle. This operation is normal.

• 25°C (77°F) Transmission Temperature

• 90°C (194°F) Transmission Temperature

Park-Transmission Oil Pump Aeration/Cavitation

Aeration is the introduction of air into the transmission fluid (pump inlet).

Erratic whining sound due to uneven distribution of air.

Cavitation occurs when cavities are formed due to a drop in fluid pressure (outlet).

Rattling, whirling/roaring or grinding sounds are all possible.

• 75°C (167°F) Pump Aeration Cavitation 900 RPM Steady State

• 75°C (167°F) Pump Aeration Cavitation 650-1500 RPM Sweep
Common Causes:

• Low fluid level

• Plugged/mis installed filter
6769556
• Torn/damaged filter O-ring

• Transmission running max line pressure due to DTCs
Bulletin No.: 24-NA-264
November, 2024
Page 3
Park Transmission Oil Pump Gear Mesh Whine

Unlike previous generation HD transmissions (6 speed), the 10 speed Allison model transmission utilizes a (3) spur

gear design (driven off of the torque converter) to drive the transmission oil pump.

Due to the 3 helical gear design, some transmissions may exhibit a whine noise while in park or driving and may get

louder as engine speed or transmission temp increases.

Isolating the whine to the oil pump gears can often be done by replicating the complaint in park and sweeping engine

speed slowly from base idle to 2500 RPM.

If whine can be reproduced in park, replacement of the transmission front support and/or transmission oil pump often

corrects the whine complaint.

Note: 4 Cylinder CSS engines (LSY/L3B) have the possibility of generating their own set of whine noises from

balance shafts/timing drives that may make isolating whine more difficult.

Park- Return to Park Blowoff Valve Chirp

Possibly described as a faint, non-rhythmic chirping sound coming from underneath the vehicle in Park only and with

engine speed ~ 1000 RPM (ETRS Only).

A Chirp noise is caused by the Return-to-Park (RTP) blow-off valve becoming unseated due to line pressure spikes.

Line pressure spikes occur because of clutch command cycling that takes place in park.

Condition is considered normal if noise occurs just off idle speed ~1000 RPM in Park Only.

Start Up/Garage Shift Clunk

Described as an infrequent audible thud that delayed 400–700ms after either a key start or garage shift event.

Severity of thud depends on the load that's placed on the driveline.

Previous root cause work determined noise is related to the C2 clutch application at high line pressure causing the

rotating components in park to stop too quickly.

C2 clutch calibration has been modified to assure the C2 knockdown area is pressurized in park and neutral when

C2 is being applied.
6769524
• Key Start

• Garage Shift
Page 4
November, 2024
Bulletin No.: 24-NA-264
Common Complaints in Drive

Reaction Gearset Whine (Gearset One)

With variation in gear tooth finish and positional control, some customers may experience whine from the reaction

planetary gearset during light to moderate driving conditions.

Most common conditions to hear whine from the reaction gearset is in 4th and 5th gear (20-35 MPH) (32-56 KPH).

Reaction gearset is active in gears 3-6 and 8-10 so depending on severity it may be possible to hear in gears other

than 4/5.

Frequency of whine will change as transmission shifts gears due to component rotation speeds being changed.

Utilizing manual tap to shift through gears is a good way to verify what gears whine in present in.

Note: Whine from the reaction gearset should not be present in 7th gear due to the 1:1 ratio and gears being locked.

If whine is present in 7th gear, issue likely lives with some other component.

Underbody Gear Rattle (7th Gear Only)
6769588
While rare, rattle during light acceleration (10–15% throttle) in 7th gear only may be observed.

Size of the idler gear inner diameter can affect the interference fit of the pressed in bearing reducing the overall

axial/radial clearance of the bearing balls.

The gear free lock will increase or decrease depending on that interference fit:

-
High interference fit can create gear rattle
-
Low interference fit does not produce rattle
Increasing line pressure can reduce rattle by overcoming the drag torque.

Note: The feature to change line pressure using Techline Connect is not active, otherwise that would be a means to

verify.
Version
1
Modified
Released November 26, 2024
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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