Mercedes-Benz bulletin ELW - M278 Cat
What it saysThis NCU replaces the prior NCU issued on May 11, 2023, and clarifies replacement part information. NHTSA’s full summary ↓
Mercedes-Benz filed this with NHTSA as a service bulletin dated Jul 27, 2023, received Aug 2, 2023, about the engine. It names 12 model years (2016–2020). 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.
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What the bulletin says
Source: NHTSA's summary of the manufacturer's communicationPicked out of NHTSA’s summary below, word for word. The document itself is the record, and the dealer checks the VIN.
This NCU replaces the prior NCU issued on May 11, 2023, and clarifies replacement part information. In our continuing efforts to assure the proper performance of Mercedes-Benz products and to enhance the satisfaction of our customers, Mercedes-Benz AG (“MBAG”), the manufacturer of Mercedes-Benz vehicles, is extending the warranty coverage on the catalytic converter system in certain Model Year (“MY”) vehicles fitted with the M278 8-cylinder engine listed below: - MY2011: Original New Vehicle Limited Warranty of 4 years / 50,000 miles New Vehicle to 13 years / 156,000 miles (whichever occurs first) - MY2012: Original New Vehicle Limited Warranty of 4 years / 50,000 miles New Vehicle to 12 years / 144,000 miles (whichever occurs first) - MY2013: Original New Vehicle Limited Warranty of 4 years / 50,000 miles New Vehicle to 11 years / 132,000 miles (whichever occurs first) - MY2014 – MY2020: Original New Vehicle Limited Warranty of 4 years / 50,000 miles New Vehicle to 10 years / 120,000 miles (whichever occurs first)
One of the 357 warranty extensions and special-coverage programs on file — every make, with the term each runs to.
Document filed under this number
| Document | Kind | Dated | NHTSA id | At NHTSA |
|---|---|---|---|---|
| ELW - M278 Cat | Service bulletin | Jul 27, 2023 | 10240203 | PDF, 210 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.
Doing the repair yourself, or pricing it before the shop does? Search the part by fitment on eBay Motors — the listing and the price are the seller’s.
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Model years it names
Source: as the manufacturer filed themA 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 12 model years this bulletin names have filed 315 complaints with NHTSA since 2015. 43 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.
Catalytic converters are factory defective My vehicle has less than 80K miles and used as pleasure vehicle. The problem has been inspected and confirmed by a reputable independent service provider. Warning lights came on and upon inspection it was determined that 3 catalytic converters are defective.
2016 Mercedes-Benz S-Class · Engine · filed with NHTSA Mar 18, 2023
Re-Seal Upper Timing Covers of the cylinder head timing covers are seeping. 2016 E350 has less thank 19k on it. The fluids can potentially leak onto the roads causing a hazard, it is also a fire hazard, as well as an environmental issue. This was identified by Revolution Mercedes in Decatur, GA.
2016 Mercedes-Benz E-Class · Engine · filed with NHTSA Oct 7, 2021
I have observed on multiple occasions when the vehicle is brought to a complete stop during driving in traffic, the engine will stall / shut off. When this occurs the engine has to be re-started with the ignition switch to be able to drive the car again.
2017 Mercedes-Benz S-Class · Engine · filed with NHTSA Nov 8, 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 engine
Source: same model, same component group52 other manufacturer communications filed against these Mercedes-Benz models under the same component group (engine), newest first. The eight newest are listed; the rest are on the Mercedes-Benz list.
| Number | Kind | Dated | NHTSA’s summary |
|---|---|---|---|
| LI01.20-P-080884 | Service bulletin | Aug 12, 2026 | Complaint Oil leaks found on M176 or M177 engines diagnosed to be from the cylinder head cover area Cause Unknown (under investigation) Reme… |
| LI07.10-P-080384 | Service bulletin | Aug 7, 2026 | Complaint Customer reports Check Engine Light with possible loss of power concern. The Following DTC's are present • P210185 - The throttle… |
| NCU - 2026010004 | Service campaign | Jul 27, 2026 | • Always use the latest XENTRY Diagnosis software release with all available add-ons. • Make sure to follow the operation steps exactly as d… |
| LI20.10-P-072886 | Service bulletin | Jul 24, 2026 | Complaint Check Engine Light ON with DTC P012800 "The Coolant Temperature is Below the Specified Temperature" active and/or stored in the ME… |
| Emissions - 2024100016 | Emissions | Jul 24, 2026 | Mercedes-Benz AG (“MBAG”), the manufacturer of Mercedes-Benz, has determined that on certain MY 2019-2021 C-Class, G-Class, GLC, GT, S-Class… |
| LI07.61-P-080241 | Service bulletin | Jun 11, 2026 | Complaint CEL ON with DTC P061197 "the control unit fuel injector has a malfunction output stage fault of control unit is restricted" active… |
| LI07.70-P-080607 | Service bulletin | Jun 3, 2026 | Complaint Check engine light activated. Fault codes related to misfire on multiple cylinders stored. Possible fault codes listed below: P030… |
| Emissions - 2026020006 | Emissions | Apr 24, 2026 | Mercedes-Benz AG, the manufacturer of Mercedes-Benz vehicles, has determined that on certain subject vehicles equipped with an 8-cylinder en… |
Quote the number at the service desk. It is what the dealer’s system is keyed on.
Every manufacturer communication NHTSA holds for Mercedes-Benz, by the number printed on the letter.
Common questions
Source: NHTSA, 49 CFR 579.5Is Mercedes-Benz ELW - M278 Cat 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 ELW - M278 Cat 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 ELW - M278 Cat cover?
The manufacturer filed it against 12 model years: 2018 Mercedes-Benz CLS-Class, 2017 Mercedes-Benz CLS-Class, 2016 Mercedes-Benz CLS-Class, 2017 Mercedes-Benz E-Class, 2016 Mercedes-Benz E-Class, 2017 Mercedes-Benz S-Class and more. Whether one particular vehicle is affected is a matter of its VIN and its build, not its model year alone.