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Service bulletin 21-NA-120

A bulletin is a manufacturer's communication to its dealers, as NHTSA indexes it. The summary is NHTSA's. The document is the manufacturer's: read it at NHTSA. A bulletin is not a recall, and listing a model year does not mean every vehicle of it is concerned.

The communication, as NHTSA indexes it (as of 2026-10-19)
TypeService bulletin
NHTSA id10243980
Published by NHTSA2023-10-14
Manufacturer's number21-NA-120
Manufacturer's date2023-09-19
NHTSA componentPOWER TRAIN; EQUIPMENT

NHTSA's summary

This service bulletin provides a Diagnostic Tip for Noise, Vibration, and/or Harshness Issues/Clunk Noise Heard During Coast Down Event after the transfer case was removed from the transmission and reinstalled during a recent repair.

The document

The document is the manufacturer's. This site does not hold it. NHTSA files a document at one of these two addresses; we have not asked NHTSA which.

Components

Equipment and accessories, Transmission and driveline

Vehicles listed
CHEVROLET SILVERADO 25002020, 2021, 2022, 2023, 2024 (the catalog's model; the bulletin names a series or trim of it)
CHEVROLET SILVERADO 35002020, 2021, 2022, 2023, 2024 (the catalog's model; the bulletin names a series or trim of it)
GMC SIERRA 25002020, 2021, 2022, 2023, 2024 (the catalog's model; the bulletin names a series or trim of it)
GMC SIERRA 35002020, 2021, 2022, 2023, 2024 (the catalog's model; the bulletin names a series or trim of it)

Listing a model year does not mean every vehicle of it is concerned: the document says which.

Recalls for the same vehicles and component
20260602026-02-12. Powertrain
26V0830002026-02-12. POWER TRAIN:AUTOMATIC TRANSMISSION:CONTROL MODULE:SOFTWARE; POWER TRAIN:AUTOMATIC TRANSMISSION:FLUID/LUBRICANT:VALVES/VALVE BODY
20246372024-10-24. Powertrain
24V7970002024-10-24. POWER TRAIN:AUTOMATIC TRANSMISSION:FLUID/LUBRICANT:VALVES/VALVE BODY; POWER TRAIN:AUTOMATIC TRANSMISSION:CONTROL MODULE:SOFTWARE
20221602022-03-31. Accessories
20205052020-10-23. Powertrain
20V6500002020-10-22. POWER TRAIN:DRIVELINE:DRIVESHAFT
20201652020-04-16. Accessories
20194942019-10-03. Accessories

A recall listed here may apply to some of the same vehicles. Only the manufacturer can say whether it applies to one vehicle.

Other bulletins for the same vehicles and component
N252502891-012026-08-20. Service campaign. Certain vehicles may have a condition in which the internal differential nut was cross threaded or missing during assembly. Dealers will review the vehicles service history in IVH, and if necessary, replace the rear electric drive transmission module.
25-NA-0802025-12-03. Service bulletin. This service bulletin provides a procedure to overhaul the control valve to replace a plate and worn down check ball to correct the customers concern of No Reverse, No Shift Past Third Gear - DTC P2732 Set.
24-NA-2622025-12-03. Service bulletin. This bulletin helps aid the tech in possible 10L100 transmission noise that may be normal or abnormal depending on the concern noted.
25-NA-1082025-10-27. Service bulletin. This bulletin provides a procedure to inspect and verify the drive shafts are over extending past the 5mm tolerance, causing the customers concern of a fluid leak under the vehicle.
25-NA-0802025-10-16. Service bulletin. This service bulletin provides a procedure to overhaul the control valve to replace a plate and worn down check ball to correct the customers concern of No Reverse, No Shift Past Third Gear - DTC P2732 Set.
N242454441 -032025-10-09. Service campaign. Certain vehicles listed above, may have a condition where the transmission control valve has worn, resulting in a gradual loss of pressure within the valve. The effects can cause harsh shifting, setting a service engine soon message, reduced engine performance or P0747 diagnostic trouble code. Dealers are to install a new control valve body. The repairs will be made at no charge to the customer.
22-NA-1822025-09-27. Service bulletin. This service bulletin advises the technician to check if the transmission cooler lines are twisted to correct customer concerns of Harsh Shift, Shudder, Surge, Stall, Transmission Overheating and/or High Transmission Fluid Temperature.
25-NA-0142025-07-08. Service bulletin. This bulletin provides a procedure to overhaul the control valve to replace a plate and worn down check ball to correct the customers concern of No Reverse, No Shift Past Third Gear - DTC P2732 Set.
24-NA-0782025-07-08. Service bulletin. This bulletin advises the tech to replace the starter and not the trans if grinding or growling is heard from the transmission area.
24-NA-0752025-07-07. Service bulletin. This bulletin provides a procedure to add a shim to the rear axle to change the pitch of said axle to correct the angle of the axle to pinion variance.