GM bulletin 20-NA-166
What it saysThis service bulletin advises the technician of possible coolant entering the areas of the engine, either through failed parts or defects in the castings, that may be the cause of the concerns related to the MIL… NHTSA’s full summary ↓
GM filed this with NHTSA as a service bulletin dated Jan 8, 2025, received Mar 29, 2024, about the engine — 2 documents under this number. It names 88 model years across Chevrolet, GMC and Cadillac (2016–2025). 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 service bulletin advises the technician of possible coolant entering the areas of the engine, either through failed parts or defects in the castings, that may be the cause of the concerns related to the MIL or the engine running rough.
Trouble codes it names: P0300 P050D all 2 read from the document itself; NHTSA’s summary names none
Documents filed under this number
| Document | Kind | Dated | NHTSA id | At NHTSA |
|---|---|---|---|---|
| 20-NA-166 | Service bulletin | Jan 8, 2025 | 11013070 | PDF, 203 KB |
| 20-NA-166 | Service bulletin | Mar 21, 2024 | 10252125 | PDF, 455 KB |
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 49 model years
and 9 more on this site: 2024 Chevrolet Tahoe, 2023 Chevrolet Tahoe, 2022 Chevrolet Tahoe, 2021 Chevrolet Tahoe, 2020 Chevrolet Tahoe, 2019 Chevrolet Tahoe, 2018 Chevrolet Tahoe, 2017 Chevrolet Tahoe, 2016 Chevrolet Tahoe.
GMC 20 model years
and 12 more on this site: 2017 GMC Sierra, 2016 GMC Sierra, 2025 GMC Yukon, 2024 GMC Yukon, 2023 GMC Yukon, 2022 GMC Yukon, 2021 GMC Yukon, 2020 GMC Yukon, 2019 GMC Yukon, 2018 GMC Yukon, 2017 GMC Yukon, 2016 GMC Yukon.
Cadillac 19 model years
and 11 more on this site: 2018 Cadillac CTS-V, 2025 Cadillac Escalade, 2024 Cadillac Escalade, 2023 Cadillac Escalade, 2022 Cadillac Escalade, 2021 Cadillac Escalade, 2020 Cadillac Escalade, 2019 Cadillac Escalade, 2018 Cadillac Escalade, 2017 Cadillac Escalade, 2016 Cadillac Escalade.
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 88 model years this bulletin names have filed 19,022 complaints with NHTSA since 2015. 7,400 of them name Engine — 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.
Car has what is called the "chevy shake" which effects almost all models from 2015-2017. Car shakes violently at times. Paid for repairs. This should be a recall as it is with other Escalade models and GM models of the same chassis..car has extreme rumble at times and is difficult to steer. While in motion at speeds of 45-70 this happens
2016 Cadillac Escalade · Engine · filed with NHTSA Jun 20, 2019 · ODI 11221462
*takata recall* I have been noticing a lot of different issues with my 2017 Tahoe premier. The engine block is a deep rust color. Engine is extremely hot even hours later after parking. There is a thick black sludge that is on nearly every part under the truck. I started hearing a ticking noise that sped up as my driving speed increases.
2017 Chevrolet Tahoe · Engine · filed with NHTSA Aug 23, 2018 · ODI 11121798
I’m filing this safety complaint in addition to a previous complaint, 11678151. which occurred on August 1, 2025. On Friday, August 22, 2025, I experienced a 2nd Traction Control alert and engine failure lights on my 2026 Sierra Denali Ultimate truck which again caused the acceleration to drastically decline while driving home from work.
2025 GMC Sierra · Engine · filed with NHTSA Aug 24, 2025 · ODI 11682678
In depth: 2024 Cadillac Escalade engine problems → · 2023 Cadillac Escalade engine problems → · 2022 Cadillac Escalade engine problems → · 2021 Cadillac Escalade engine 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 engine
Source: same model, same component group236 other manufacturer communications filed against these GM models under the same component group (engine), newest first. The eight newest are listed; the rest are on the Chevrolet list.
| Number | Kind | Dated | NHTSA’s summary |
|---|---|---|---|
| N262576260 | Service campaign | Oct 15, 2026 | General Motors has decided to conduct a Voluntary Emission Recall. Certain vehicles may have a condition that could cause a small exhaust le… |
| N262568830 | Service campaign | Aug 4, 2026 | Certain vehicles listed above may have a condition in which the oil filter was not adequately tightened. Dealers are to check and tighten th… |
| N262552620 | Service campaign | May 11, 2026 | Certain vehicles may have a condition that could cause the cylinder 2 glow plug to fail. If this failure occurs, the Malfunction Indicator… |
| N262552610 | Service campaign | May 7, 2026 | Certain vehicles may have a condition that could cause the crankcase pressure sensor to fail. If this failure occurs, the Malfunction Indic… |
| N262548050 | Service campaign | Apr 24, 2026 | Certain vehicles, may have a condition that could cause the Catalytic Converter to fail. If this failure occurs, the Malfunction Indicator L… |
| N252494003-02 | Service campaign | Jan 21, 2026 | Certain vehicles listed above, may have a condition where the connecting rod and/or crankshaft engine components in these vehicles may have… |
| 25-NA-339 | Service bulletin | Nov 6, 2025 | Under Field Actions N252494000, N252494001, the service procedure includes performing a PICO test on vehicle engines within the identified s… |
| N252508341 | Service campaign | Sep 16, 2025 | Certain vehicles listed above, may have a condition that could cause the engine coolant control valve to fail an onboard vehicle diagnostic… |
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 20-NA-166 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-166 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-166 cover?
The manufacturer filed it against 88 model years across 3 brands (Chevrolet, GMC and Cadillac): 2025 Cadillac CT5, 2024 Cadillac CT5, 2023 Cadillac CT5, 2022 Cadillac CT5, 2019 Cadillac CTS, 2018 Cadillac CTS and more. Whether one particular vehicle is affected is a matter of its VIN and its build, not its model year alone.