Mercedes-Benz bulletin LI20.30-P-078666
What it saysComplaint Coolant level warning in instrument cluster. NHTSA’s full summary ↓
Mercedes-Benz filed this with NHTSA as a service bulletin dated Sep 25, 2025, received Dec 23, 2024, about the engine — 3 documents under this number. It names 2 model years (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.
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What the bulletin says
Source: NHTSA's summary of the manufacturer's communicationComplaint Coolant level warning in instrument cluster. Coolant odor or leaking from coolant expansion reservoir. Cause Coolant wicking through electrical contacts, or level sensor electrical connections not present in expansion reservoir. Remedy **Important: If the coolant expansion tank is replaced due to leak at the level sensor contact area, ensure that the expansion tank is marked as the main damage part in the warranty claim 1- Inspect expansion tank level sensor electrical connection for missing contacts. Additionally the triangular sticker may not be present on top of reservoir. See example of OK and NOK part. • Replace the expansion reservoir if contacts are found to be missing. A TIPS case is not needed. • Proceed to step 3. 2- With contacts present, inspect coolant level sensor electrical connection for leakage past contact seals. Visible coolant at the connection indicates leakage. • Capture photos if leakage is identified and create a TIPS case with the Powertrain team. • Replace the expansion reservoir. 3- Repair any damage to wiring or electrical contacts on wiring harness from S41 to N10/6. • Check the front SAM N10/6 for coolant contamination and replace if necessary. • Inspect electrical connectors at base of A-pillar for contamination and repair/replace as necessary.
Documents filed under this number
| Document | Kind | Dated | NHTSA id | At NHTSA |
|---|---|---|---|---|
| LI20.30-P-078666 | Service bulletin | Sep 25, 2025 | 11023363 | PDF, 5,123 KB |
| LI20.30-P-078666 | Service bulletin | Jul 29, 2025 | 11021105 | PDF, 38 KB |
| LI20.30-P-078666 | Service bulletin | Dec 19, 2024 | 11012053 | PDF, 38 KB |
What the document itself lists
Part the bulletin names
| Part number | Description | Qty | Find it |
|---|---|---|---|
| A1675009900 | Coolant expansion reservoir 1 X | — | eBay Motors → |
Read by machine from the document NHTSA serves (4 pages), read Sep 30, 2026. A part number is shown only where it matches Mercedes-Benz’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 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 2 model years this bulletin names have filed 46 complaints with NHTSA since 2015. 8 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.
Radiator started leaking in <3000 miles of driving the brand new GLE 580 Mercedes Benz. Twice I got errors in the car that stated check coolant level I could hear liquid moving in the front of the car when I parked it. Once while driving, the AC totally stopped working and on the entire drive, I couldn't feel the cool air.
2025 Mercedes-Benz GLE-Class · Engine · filed with NHTSA Jan 25, 2026 · ODI 11713270
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 group39 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 |
|---|---|---|---|
| LI18.00-P-073137 | Service bulletin | Sep 26, 2026 | Complaint Sporadic warning message in instrument cluster "Engine oil pressure stop switch off vehicle" (or similar) is shown in red on vehi… |
| LI20.10-P-075374 | Service bulletin | Sep 17, 2026 | Complaint Red coolant warning in instrument cluster. Fault codes U019F00 or U019F87 current/stored in MRG1 control unit. Cause Various cause… |
| 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… |
| 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… |
| LI01.30-P-072328 | Service bulletin | Mar 27, 2026 | Complaint -Check engine light illuminated. -Engine runs rough. -Poor shifting or jerking when accelerating. -Fault codes stored related to m… |
| CL - EW M157 | Other | Mar 27, 2026 | Dear Mercedes-Benz Owner: In our continuing efforts to ensure the proper performance of Mercedes-Benz products and to enhance the satisfacti… |
| EW - Vacuum Pump M157 | Warranty extension | Mar 14, 2026 | In our continuing efforts to ensure the proper performance of Mercedes-Benz products and to enhance the satisfaction of our customers, Merce… |
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 LI20.30-P-078666 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 LI20.30-P-078666 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 Mercedes-Benz warranty extension on file lists the ones Mercedes-Benz has filed.
Which vehicles does LI20.30-P-078666 cover?
The manufacturer filed it against 2 model years: 2025 Mercedes-Benz GLE-Class, 2025 Mercedes-Benz GLS-Class. Whether one particular vehicle is affected is a matter of its VIN and its build, not its model year alone.