GM bulletin 21-NA-155
What it saysThis informational bulletin advises the technician to check for faults that may be caused by the trailer other wise found by a possible faulty trailer connector. NHTSA’s full summary ↓
GM filed this with NHTSA as a service bulletin dated Jan 17, 2025, received Jul 1, 2022, about the electrical system — 4 documents under this number. It names 58 model years across Chevrolet, GMC and Cadillac (2019–2025). 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 · Cadillac.
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What the bulletin says
Source: NHTSA's summary of the manufacturer's communicationThis informational bulletin advises the technician to check for faults that may be caused by the trailer other wise found by a possible faulty trailer connector.
Trouble codes it names: C1114 all 1 read from the document itself; NHTSA’s summary names none
Documents filed under this number
| Document | Kind | Dated | NHTSA id | At NHTSA |
|---|---|---|---|---|
| 21-NA-155 | Service bulletin | Jan 17, 2025 | 11013242 | PDF, 261 KB |
| 21-NA-155 | Service bulletin | Apr 8, 2024 | 10253528 | PDF, 184 KB |
| 21-NA-155 | Service bulletin | Jan 11, 2024 | 10249034 | PDF, 187 KB |
| 21-NA-155 | Service bulletin | Jun 14, 2022 | 10214860 | PDF, 3,329 KB |
What the document itself lists
Part the bulletin names
| Part number | Description | Qty | Find it |
|---|---|---|---|
| 84056018 | Trailer Side Customer Recommendation | — | eBay Motors → |
Labour operation and the time the manufacturer allows
| Operation | Description | Time |
|---|---|---|
| 5486198 | Tow Vehicle Electrical Receptacle Diagnostic | 0.3 hrs |
Read by machine from the document NHTSA serves (6 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 29 model years
GMC 24 model years
and 13 more on this site: 2021 GMC Sierra 2500HD, 2020 GMC Sierra 2500HD, 2025 GMC Sierra 3500HD, 2024 GMC Sierra 3500HD, 2023 GMC Sierra 3500HD, 2022 GMC Sierra 3500HD, 2021 GMC Sierra 3500HD, 2020 GMC Sierra 3500HD, 2025 GMC Yukon, 2024 GMC Yukon, 2023 GMC Yukon, 2022 GMC Yukon, 2021 GMC Yukon.
Cadillac 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 58 model years this bulletin names have filed 12,811 complaints with NHTSA since 2015. 2,928 of them name Electrical System, Service Brakes, Equipment — 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 2019 Chevrolet Silverado, the 122 owners who gave an odometer reading for Service Brakes reported it at a median of 8,000 miles. That figure is one model year’s, not the whole range this bulletin covers — medians from different model years are not averaged.
Bought new and there was a brake pad sensor message immediately that we took it to the dealer several times for and nothing was done other than clearing the code and giving it back. Was in accident 1/24 and it was found that there was a frayed/damaged wire in the break module and break pad sensor that I feel could have led to the accident
2023 Chevrolet Tahoe · Service Brakes · filed with NHTSA Apr 2, 2024 · ODI 11580791
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
After the latest update from the Dealer, the integrated trailer brake module no longer shows an output of how much power it's applying to the trailer brake system. It just stays blank. I can tell that the brakes actually are being applied, however not having indication of them being applied and how much pressure is applied is concerning
2024 GMC Sierra · Service Brakes · filed with NHTSA Jun 2, 2026 · ODI 11741595
In depth: 2024 Chevrolet Silverado electrical problems → · 2023 Chevrolet Silverado electrical problems → · 2022 Chevrolet Silverado electrical problems → · 2022 Chevrolet Silverado brake 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 electrical system
Source: same model, same component group311 other manufacturer communications filed against these GM models under the same component group (electrical system), newest first. The eight newest are listed; the rest are on the Chevrolet list.
| Number | Kind | Dated | NHTSA’s summary |
|---|---|---|---|
| N262565450 | Service campaign | Oct 26, 2026 | Customer Satisfaction Program. Certain vehicles listed above may have a condition in which remanufactured high voltage battery packs were b… |
| N252529080 | Service campaign | Apr 1, 2026 | Service Update. Certain vehicles listed above may be missing a high voltage header plug on the RESS battery pack drive motor connector. Dea… |
| N252515590 | Service campaign | Jan 27, 2026 | Certain vehicles listed above, may have a condition in which the body-to-chassis ground strap may be corroded. Dealers will replace the grou… |
| 18-NA-180 | Service bulletin | Sep 4, 2025 | This Warranty Administration service bulletin provides Lithium-Ion battery Exchange Process and Transaction Submission information. |
| 25-NA-021 | Service bulletin | Jun 7, 2025 | This technical bulletin provides repair information to correct a customer concern of Radio Software Update W23E-178.1.2-M174-SQBR6-93.3. |
| 25-NA-153 | Service bulletin | Jun 5, 2025 | This informational bulletin provides Information on Rear Upper Body Structure Auxiliary Lamp Will Not Turn ON. |
| 22-NA-083 | Service bulletin | May 17, 2025 | This service bulletin provides Requirements for Replacement of the Dual Mode Cord Set Under Warranty. |
| 25-NA-131 | Service bulletin | May 17, 2025 | This Service bulletin provides information on the heated seats warming up when the vehicle is started but soon cooling off and the heated se… |
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-155 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-155 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-155 cover?
The manufacturer filed it against 58 model years across 3 brands (Chevrolet, GMC and Cadillac): 2025 Cadillac Escalade, 2024 Cadillac Escalade, 2023 Cadillac Escalade, 2022 Cadillac Escalade, 2021 Cadillac Escalade, 2025 Chevrolet Silverado and more. Whether one particular vehicle is affected is a matter of its VIN and its build, not its model year alone.