GM bulletin 20-NA-121
What it saysThis service bulletin provides a procedure to locate and fix a possible leak in the roof area due to missing sealant to correct customer concerns of Various Electrical Issues, No Start, Stall, Brake Lamp Not Off, Radio… NHTSA’s full summary ↓
GM filed this with NHTSA as a service bulletin dated Feb 27, 2024, received Mar 6, 2024, about the service brakes. It names 9 model years across Chevrolet and Buick (2020–2024). 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 · Buick.
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What the bulletin says
Source: NHTSA's summary of the manufacturer's communicationThis service bulletin provides a procedure to locate and fix a possible leak in the roof area due to missing sealant to correct customer concerns of Various Electrical Issues, No Start, Stall, Brake Lamp Not Off, Radio Inoperative, Remote Key Inoperative, Malfunction Indicator Lamp (MIL) Illuminated with Possible DTCs.
Trouble codes it names: C0750 C0755 C0760 C0765 all 4 read from the document itself; NHTSA’s summary names none
Document filed under this number
| Document | Kind | Dated | NHTSA id | At NHTSA |
|---|---|---|---|---|
| 20-NA-121 | Service bulletin | Feb 27, 2024 | 10251350 | PDF, 263 KB |
What the document itself lists
The manufacturer titles it “Water Leak at Roof Area, Various Electrical Issues, No Start, Stall, Brake Lamp Not Off,”.
Part the bulletin names
| Part number | Description | Qty | Find it |
|---|---|---|---|
| 18920104 | — | — |
Labour operation and the time the manufacturer allows
| Operation | Description | Time |
|---|---|---|
| 1481498 | Inspect/Clean Body-IP Inline Connectors, Seat Belt Retractor Pretensioners and Body… | 1.2 hrs |
Read by machine from the document NHTSA serves (7 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 4 model years
Buick 5 model years
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 9 model years this bulletin names have filed 654 complaints with NHTSA since 2015. 263 of them name Electrical System, Service Brakes, Wheels — 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 Buick Encore, the 14 owners who gave an odometer reading for Service Brakes reported it at a median of 1,476 miles. That figure is one model year’s, not the whole range this bulletin covers — medians from different model years are not averaged.
The brakes squeak constantly and occasionally skid or lock up. The car will occasionally have all electrical power disconnected so all screens go blank for 2-3 secs (sometimes in succession for 3 times max), the car will continue to run and drive. However, the screens will blink as if starting up each time the car does this.
2024 Buick Encore · Service Brakes · filed with NHTSA Oct 23, 2025
I bought my car, new, on 10/1/ 2023. The middle of November i noticed the headlights randomly dimming. On 12/3/23 I to the dealership to have them looked at. I was told there was nothing wrong but make an appt. they had my car 3 times in less than 2 months. I repeatedly told them my headlights were dimming and or going off.
2023 Buick Encore · Electrical System · filed with NHTSA Apr 26, 2024
The contact owns a 2021 Chevrolet Trailblazer. The contact stated that while driving at various speeds, the vehicle made an abnormal popping sound before the power steering and brakes failed. Additionally, the brake pedal became extremely sensitive while gently being depressed causing the vehicle to abruptly stop.
2021 Chevrolet Trailblazer · Electrical System · filed with NHTSA Nov 18, 2021
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 service brakes
Source: same model, same component group6 other manufacturer communications filed against these GM models under the same component group (service brakes), newest first.
| Number | Kind | Dated | NHTSA’s summary |
|---|---|---|---|
| 24-NA-048 | Service bulletin | Feb 6, 2025 | This engineering informational bulletin is requesting information from technicians to perform the check list provided and contact the engine… |
| 24-NA-072 | Service bulletin | Nov 8, 2024 | This technical bulletin provides a procedure a squeal noise heard from the front of the vehicle during light brake pedal application. |
| PIC5704H | Service bulletin | Feb 19, 2024 | This Preliminary Information communication provides information to the technician about vehicles that had the Brake Pressure Modulator Valve… |
| 19-NA-223 | Service bulletin | Oct 3, 2023 | This service bulletin provides information for dealers/technicians on a normal characteristic of Brake Pedal - Excessive Click Noise with Sl… |
| 22-NA-095 | Service bulletin | Oct 2, 2023 | This service bulletin provides repair information to correct a customer concern of hearing a front brake squeal noise during light brake ped… |
| 22-NA-097 | Service bulletin | Sep 19, 2023 | This technical bulletin provides a procedure to test and replace the brake pedal to correct a customer concern that the cruise control will… |
Quote the number at the service desk. It is what the dealer’s system is keyed on.
Every manufacturer communication NHTSA holds for Chevrolet and Buick, by the number printed on the letter.
Common questions
Source: NHTSA, 49 CFR 579.5Is GM 20-NA-121 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 20-NA-121 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.
Which vehicles does 20-NA-121 cover?
The manufacturer filed it against 9 model years across 2 brands (Chevrolet and Buick): 2024 Buick Encore, 2023 Buick Encore, 2022 Buick Encore, 2021 Buick Encore, 2020 Buick Encore, 2024 Chevrolet Trailblazer and more. Whether one particular vehicle is affected is a matter of its VIN and its build, not its model year alone.