GM bulletin 21-NA-181
What it saysThis service bulletin provides 9th gear operation information to respond to customers that may comment on transmission shift operation. NHTSA’s full summary ↓
GM filed this with NHTSA as a service bulletin dated Nov 18, 2024, received Apr 21, 2022, about the power train — 4 documents under this number. It names 52 model years across Chevrolet, GMC, Buick and Cadillac (2018–2025). 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 · Buick · Cadillac.
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What the bulletin says
Source: NHTSA's summary of the manufacturer's communicationThis service bulletin provides 9th gear operation information to respond to customers that may comment on transmission shift operation.
Documents filed under this number
| Document | Kind | Dated | NHTSA id | At NHTSA |
|---|---|---|---|---|
| 21-NA-181 | Service bulletin | Nov 18, 2024 | 11011904 | PDF, 124 KB |
| 21-NA-181 | Service bulletin | Aug 8, 2023 | 10242106 | PDF, 494 KB |
| 21-NA-181 | Service bulletin | Aug 29, 2022 | 10219391 | PDF, 69 KB |
| 21-NA-181 | Service bulletin | Apr 8, 2022 | 10210404 | PDF, 69 KB |
What the document itself lists
Labour operation and the time the manufacturer allows
| Operation | Description | Time |
|---|---|---|
| 8486038 | Confirm 9TH Gear Operation | 0.3 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 11 model years
GMC 11 model years
Buick 11 model years
Cadillac 19 model years
and 11 more on this site: 2024 Cadillac XT5, 2023 Cadillac XT5, 2022 Cadillac XT5, 2021 Cadillac XT5, 2020 Cadillac XT5, 2025 Cadillac XT6, 2024 Cadillac XT6, 2023 Cadillac XT6, 2022 Cadillac XT6, 2021 Cadillac XT6, 2020 Cadillac XT6.
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 52 model years this bulletin names have filed 2,975 complaints with NHTSA since 2015. 560 of them name Power Train — 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 2018 GMC Terrain, the 23 owners who gave an odometer reading for Power Train reported it at a median of 10,300 miles. That figure is one model year’s, not the whole range this bulletin covers — medians from different model years are not averaged.
I was in slow traffic and my check engine light came on then the parking brake engaged. My car stopped and I could not disengage the parking brake so the car could shift gears. I turned my car off for several minutes. When I turned the car back on, the check engine light and parking brake turned off and I was able to shift gears again
2020 Cadillac XT4 · Power Train · filed with NHTSA Mar 27, 2025 · ODI 11651144
On 4/14 with only 21 miles on the odometer in this newly purchased car the entire transmission failed, per the dealership because of a “leaking valve”. The check engine light came on after the car was jumpy and then the car refused to speed up on an extremely busy street and began locking up, putting us at serious risk of an accident.
2025 Chevrolet Trailblazer · Power Train · filed with NHTSA May 19, 2025 · ODI 11661889
Transmission dropped complete out of gear while driving. Got vehicle moving again. Took to dealership. Found complete internal transmission failure at 6779 miles. Transmission replaced with new unit. New transmission has erratic / hard shifts. Found replacement transmission leaking fluid due to front pump / porous case at 14800 miles.
2024 GMC Terrain · Power Train · filed with NHTSA Feb 2, 2026 · ODI 11714938
In depth: 2020 Chevrolet Blazer transmission and drivetrain problems → · 2019 GMC Terrain 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 group83 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 |
|---|---|---|---|
| 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… |
| N252502890-01 | 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… |
| N242471460-01 | Service campaign | Aug 20, 2026 | Certain vehicles may have been built with an Electric Drive Unit mounting bolt that is too long, causing damage to the Drive Unit case. Deal… |
| PIE0814B | Service bulletin | May 7, 2025 | This engineering information (EI) closure ends the need for requesting further information from technicians in regard to the Service AWD Lam… |
| PIP6036A | Service bulletin | Apr 2, 2025 | This Preliminary information communicates diagnostic aids for a surge or fishbite concern |
| 25-NA-001 | Service bulletin | Mar 13, 2025 | This service bulletin provides repair information to correct a customer concern of a transmission fluid leak. |
| PIE0814A | Service bulletin | Mar 12, 2025 | This engineering information (EI) is requesting information from technicians to perform the check list provided and contact the engineer lis… |
| 24-NA-232 | Service bulletin | Mar 7, 2025 | This technical bulletin provides repair information to correct a customer concern of Metallic Noise from Rear Differential on Acceleration. |
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, Buick and Cadillac, by the number printed on the letter.
Common questions
Source: NHTSA, 49 CFR 579.5Is GM 21-NA-181 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-181 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-181 cover?
The manufacturer filed it against 52 model years across 4 brands (Chevrolet, GMC, Buick and Cadillac): 2025 Buick Encore, 2024 Buick Encore, 2023 Buick Encore, 2022 Buick Encore, 2021 Buick Encore, 2020 Buick Encore and more. Whether one particular vehicle is affected is a matter of its VIN and its build, not its model year alone.