GM bulletin 21-NA-275
What it saysThis 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… NHTSA’s full summary ↓
GM filed this with NHTSA as a service bulletin dated Nov 27, 2024, received Jun 4, 2022, about the power train — 5 documents under this number. It names 25 model years across Chevrolet, GMC and Cadillac (2019–2021). A service bulletin is not a safety recall: it is the manufacturer telling its dealers how to diagnose or repair a condition, and whether the work is paid for depends on the warranty in force. Quoting the number at a service desk can save a diagnosis.
One page for every brand it was filed under. Each brand’s bulletins: Chevrolet · GMC · Cadillac.
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What the bulletin says
Source: NHTSA's summary of the manufacturer's communicationThis 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.
Documents filed under this number
| Document | Kind | Dated | NHTSA id | At NHTSA |
|---|---|---|---|---|
| 21-NA-275 | Service bulletin | Nov 27, 2024 | 11011993 | PDF, 131 KB |
| 21-NA-275 | Service bulletin | Sep 25, 2024 | 11009463 | PDF, 131 KB |
| 21-NA-275 | Service bulletin | Oct 10, 2023 | 10244949 | PDF, 52 KB |
| 21-NA-275 | Service bulletin | Aug 23, 2022 | 10219291 | PDF, 52 KB |
| 21-NA-275 | Service bulletin | May 19, 2022 | 10213229 | PDF, 514 KB |
What the document itself lists
Parts the bulletin names
| Part number | Description | Qty | Find it |
|---|---|---|---|
| 24047734 | N/A SEAL, A/TRNS AUX FLUID PUMP | 1 | eBay Motors → |
| 19352619 | — | — | |
| 19352620 | — | — |
Labour operations and the time the manufacturer allows
| Operation | Description | Time |
|---|---|---|
| 8486158 | Test Drive/Diagnostic/Control Valve Body Replace CT | 2.2 hrs |
| 2500H | — | 1.8 hrs |
Read by machine from the document NHTSA serves (2 pages), read Sep 30, 2026. A part number is shown only where it matches GM’s own catalogue shape, an operation only with its code and time, and a description only where the reader got it whole; anything it could not settle is left out, and the PDF is the record. Times are the manufacturer’s warranty allowances, not a quote. Listings and prices on eBay Motors are the seller’s.
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The summary is NHTSA’s abstract of the document, as filed under 49 CFR 579.5. One communication is usually filed as several documents — the bulletin, a dealer notice, an owner letter — and the number on any of them finds this page. A PDF link is shown only once NHTSA’s own server has been seen to serve that document; the rest are checked over the following nights. Quote the number at a service desk; it is what the dealer’s system is keyed on.
Model years it names
Source: as the manufacturer filed themChevrolet 10 model years
GMC 7 model years
Cadillac 8 model years
Also filed against model years this site has no page for: 2021 Cadillac CT6.
A vehicle page’s bulletin list shows the newest few communications filed against that model year; the count there is every one.
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What owners reported
Source: NHTSA complaint databaseOwners of the 24 model years this bulletin names have filed 4,773 complaints with NHTSA since 2015. 1,528 of them name Power Train, Service Brakes, Air Bags — the same broad component group this bulletin is filed under. NHTSA groups complaints coarsely, so that means the same area of the vehicle, not necessarily the same fault.
On the 2020 Chevrolet Silverado, the 50 owners who gave an odometer reading for Power Train reported it at a median of 61,200 miles. That figure is one model year’s, not the whole range this bulletin covers — medians from different model years are not averaged.
My vehicle inadvertently locks the rear tires at highway speeds and then releases and drives. In some instances it may brake several times causing the tires to burn rubber for a short distance causing rear traffic to either swerve to avoid rear ending me and in a couple instances causes the rear following traffic to abruptly change lanes…
2020 GMC Sierra 2500HD · Service Brakes · filed with NHTSA Mar 29, 2024 · ODI 11580026
The contact owns a 2020 Cadillac CT6. The contact stated while driving 65 MPH, the transmission seized, and the vehicle was coasted over to the right side of the roadway while waiting for tow service. A dealer as contacted. The vehicle was towed to the dealer where it was diagnosed with transmission failure. The vehicle was not repaired.
2020 Cadillac CT6 · Power Train · filed with NHTSA Jul 15, 2025 · ODI 11673799
The contact owns a 2020 Cadillac CT6. The contact received notification of NHTSA Campaign Number: 25V148000 (Power Train); however, the part to do the recall repair was unavailable. The contact stated that while his wife was driving at an undisclosed speed, the vehicle jerked before slamming into gear. No warning lights were illuminated.
2020 Cadillac CT6 · Power Train · filed with NHTSA Jun 17, 2025 · ODI 11667446
In depth: 2021 Chevrolet Silverado transmission and drivetrain problems → · 2020 Chevrolet Silverado transmission and drivetrain problems → · 2020 Chevrolet Silverado brake problems → · 2021 Chevrolet Tahoe transmission and drivetrain problems →
A complaint is one owner’s account, not a defect finding, and a bulletin is not a recall. Nothing here says this bulletin was issued because of these complaints, or that the repair it describes fixed them. Complaint files on this site begin in 2015.
More bulletins about the power train
Source: same model, same component group132 other manufacturer communications filed against these GM models under the same component group (power train), newest first. The eight newest are listed; the rest are on the Chevrolet list.
| Number | Kind | Dated | NHTSA’s summary |
|---|---|---|---|
| N262567720 | Service campaign | Sep 17, 2026 | Certain vehicles may have received transmission mounting bolts that do not meet expected hardness specifications. Loose or failed bolts may… |
| N252502891-01 | Service campaign | Aug 20, 2026 | Certain vehicles may have a condition in which the internal differential nut was cross threaded or missing during assembly. Dealers will rev… |
| N262560680 | Service campaign | Jun 10, 2026 | Certain vehicles may have a condition in which the bolts for the transmission control valve body may be loose or missing. Dealers will retor… |
| N252517790 | Service campaign | Oct 14, 2025 | Certain vehicles, equipped with 8L80 or 8L90 Transmissions, may have a condition in which the reaction carrier cracks. Dealers are to replac… |
| N242454441 -03 | Service campaign | Oct 9, 2025 | Certain vehicles listed above, may have a condition where the transmission control valve has worn, resulting in a gradual loss of pressure w… |
| 25-NA-080 | Service bulletin | Sep 4, 2025 | This service bulletin provides a procedure to overhaul the control valve to replace a plate and worn down check ball to correct the customer… |
| N252494003-01 | Service campaign | Jun 26, 2025 | Certain vehicles listed above, may have a condition where the connecting rod and/or crankshaft engine components in these vehicles may have… |
| 24-NA-262 | Service bulletin | Jun 3, 2025 | This bulletin helps aid the tech in possible 10L100 transmission noise that may be normal or abnormal depending on the concern noted. |
Quote the number at the service desk. It is what the dealer’s system is keyed on.
Every manufacturer communication NHTSA holds for Chevrolet, GMC and Cadillac, by the number printed on the letter.
Common questions
Source: NHTSA, 49 CFR 579.5Is GM 21-NA-275 a recall?
No. A service bulletin is a manufacturer communication filed with NHTSA under 49 CFR 579.5; a safety recall carries an NHTSA campaign number (two digits, a letter, six digits) and a federal duty to repair for free. Check the vehicle’s recalls by VIN at nhtsa.gov/recalls, or on its page here.
Is the 21-NA-275 repair free?
Not automatically. A service bulletin describes how to diagnose or repair a condition; who pays depends on the warranty in force, any extension, and the dealer. Quoting the number can save a diagnosis either way. Every GM warranty extension on file lists the ones GM has filed.
Which vehicles does 21-NA-275 cover?
The manufacturer filed it against 25 model years across 3 brands (Chevrolet, GMC and Cadillac): 2021 Cadillac CT4, 2020 Cadillac CT4, 2021 Cadillac CT5, 2020 Cadillac CT5, 2020 Cadillac CT6, 2019 Cadillac CT6 and more. Whether one particular vehicle is affected is a matter of its VIN and its build, not its model year alone.