GM bulletin 20-NA-100
What it saysThis informational bulletin provides information for dealers/technicians on Engine Control Module Calibration for T1 L3B Engine with DTC P26BB Set. NHTSA’s full summary ↓
GM filed this with NHTSA as a service bulletin dated Aug 30, 2023, received Sep 15, 2023, about the electrical system. It names 4 model years across Chevrolet and GMC (2019–2020). 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.
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What the bulletin says
Source: NHTSA's summary of the manufacturer's communicationThis informational bulletin provides information for dealers/technicians on Engine Control Module Calibration for T1 L3B Engine with DTC P26BB Set.
Trouble codes it names: P26BB
Document filed under this number
| Document | Kind | Dated | NHTSA id | At NHTSA |
|---|---|---|---|---|
| 20-NA-100 | Service bulletin | Aug 30, 2023 | 10242265 | PDF, 145 KB |
What the document itself lists
The manufacturer titles it “Engine Control Module Calibration for T1 L3B Engine with DTC P26BB Set”.
Labour operation and the time the manufacturer allows
| Operation | Description | Time |
|---|---|---|
| 2886808 | Engine Control Module Reprogramming with SPS for software anomaly | 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 2 model years
GMC 2 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 4 model years this bulletin names have filed 3,030 complaints with NHTSA since 2015. 1,816 of them name Engine, Electrical System — 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 143 owners who gave an odometer reading for Engine reported it at a median of 71,000 miles. That figure is one model year’s, not the whole range this bulletin covers — medians from different model years are not averaged.
The contact owned a 2020 GMC Sierra Denali. The contact stated that while the vehicle was parked, there was an abnormal knocking sound coming from the engine compartment. The check engine warning light was intermittently illuminated. The vehicle was taken to a dealer; however, the cause of the failure was not yet determined.
2020 GMC Sierra · Engine · filed with NHTSA Sep 11, 2026 · ODI 11763621
The contact owns a 2020 GMC Sierra Denali. The contact stated while driving 65 MPH at night, the vehicle stalled and the “Shift to Neutral and Restart Vehicle” message was displayed. The contact was unable to restart the vehicle and was unable to visibly see the roadway. The contact was able to park on the side of the road.
2020 GMC Sierra · Electrical System · filed with NHTSA Apr 26, 2023 · ODI 11519126
This is my second compliant, on 5/7/20, after my shift ended. The truck would not start. I call the sales person, we went over several steps and it still would not start. I called on star. She said will do a diagnostic. When she started every thing well out. I call back by phone after an half hour..they sent me a jumper.
2020 Chevrolet Silverado · Electrical System · filed with NHTSA May 12, 2020 · ODI 11324334
In depth: 2020 Chevrolet Silverado engine problems → · 2020 Chevrolet Silverado electrical problems → · 2019 Chevrolet Silverado engine problems → · 2019 Chevrolet Silverado electrical 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 group221 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. |
| 22-NA-083 | Service bulletin | May 17, 2025 | This service bulletin provides Requirements for Replacement of the Dual Mode Cord Set Under Warranty. |
| 23-NA-151 | Service bulletin | May 16, 2025 | This service bulletin and criteria within are to determine the internal state of the High Voltage Battery and core return shipping method. |
| PIE0753I | Service bulletin | May 15, 2025 | This engineering information (EI) will assist GM to recover a small number of electric vehicle battery packs from customer-owned vehicles in… |
| 25-NA-044 | Service bulletin | May 14, 2025 | This service bulletin provides information for dealers/technicians on SPS2 Hybrid/EV Battery Data Retrieval for Service High Voltage DTCs. |
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 GMC, by the number printed on the letter.
Common questions
Source: NHTSA, 49 CFR 579.5Is GM 20-NA-100 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-100 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 20-NA-100 cover?
The manufacturer filed it against 4 model years across 2 brands (Chevrolet and GMC): 2020 Chevrolet Silverado, 2019 Chevrolet Silverado, 2020 GMC Sierra, 2019 GMC Sierra. Whether one particular vehicle is affected is a matter of its VIN and its build, not its model year alone.