Mercedes-Benz bulletin LI01.00-P-078171
What it saysComplaint Dull thumping noise or ticking noise under the vehicle in the area of the engine/two-mass flywheel/transmission. NHTSA’s full summary ↓
Mercedes-Benz filed this with NHTSA as a service bulletin dated Jan 12, 2026, received Aug 21, 2024, about the engine — 2 documents under this number. It names 6 model years (2024–2026). 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 Dull thumping noise or ticking noise under the vehicle in the area of the engine/two-mass flywheel/transmission. Is significantly perceptible at the front right wheel well and can also be faintly heard in the vehicle interior. Cause The ticking noise occurs in idle operation in drive program C (when the combustion engine is running) & S at 780 rpm when the state of charge of the battery is under 25% and the load requirement at the belt-driven starter alternator is simultaneously over 25 Nm. The load requirement can occur due to high basic consumers (e.g. electric refrigerant compressor, high-voltage booster heater or DC/DC converter) and auxiliary consumers (e.g. air conditioning system, steering wheel or seat heating, etc.). Remedy Current production configuration Do not replace any parts Create TIPS case and send to HQ together with the following documents: • Videos of the problem from the exterior and in the vehicle interior • Control unit log, engine N3/10 (ME) • Control unit log, drivetrain N127 (PTCU) • Control unit log, battery management system N82/10 (BMS) • Control unit log, DC/DC converter N83/1 (DDW) • Control unit log, electronic ignition lock N73 (EZS)
Documents filed under this number
| Document | Kind | Dated | NHTSA id | At NHTSA |
|---|---|---|---|---|
| LI01.00-P-078171 | Service bulletin | Jan 12, 2026 | 11027595 | PDF, 37 KB |
| LI01.00-P-078171 | Service bulletin | Aug 8, 2024 | 11006540 | PDF, 35 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 themAlso filed against model years this site has no page for: 2024 Mercedes-Benz AMG C63 S E; 2024 Mercedes-Benz AMG C63 S E 4MATIC+.
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 68 complaints with NHTSA since 2015. 11 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.
Brand new car Engine light also went on and off 3 or more times in one day, car had a charging failure wouldn't charge - Sold me an unsafe vehicle to drive - shaking tires, steering wheel, Car also has 13 codes including engine and transmission failure communication codes - multiple attempts to resolve the matter and the service team…
2026 Mercedes-Benz GLC-Class · Engine · filed with NHTSA Jan 6, 2026 · ODI 11709067
Vehicle experiences a severe, abrupt jerk/jolt during deceleration around the 5th-to-4th gear downshift. The issue occurs consistently when slowing down. Dealership verified the condition on Repair Order #1906625 and confirmed a transmission flaw. Dealer stated software is required from the manufacturer with no ETA for release.
2025 Mercedes-Benz GLC-Class · Power Train · filed with NHTSA Aug 6, 2026 · ODI 11755359
While at a stop with foot on brake, the vehicle surges forward powerfully making a loud noise despite having foot on brake. Forcefully pushing on brake pedal harder eventually stops the car. Most recent time the display screen showed "Transmission Deactivated". Dealership drove car once but did not perform service inspection.
2026 Mercedes-Benz GLC-Class · Power Train · filed with NHTSA Jan 16, 2026 · ODI 11711555
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 group42 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 |
|---|---|---|---|
| PSL-NCU Return Parts 8/14 | Other | Aug 15, 2026 | Dear Mercedes-Benz USA Dealers, The part numbers listed in the chart below should no longer be installed, and any existing stock must be ret… |
| 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… |
| 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… |
| LI05.20-P-080329 | Service bulletin | Mar 9, 2026 | Complaint Engine vibrations perceived at low rpm. Fault codes for the camshaft position of the intake camshaft (P001100, P001104, P001200) o… |
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 LI01.00-P-078171 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 LI01.00-P-078171 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 LI01.00-P-078171 cover?
The manufacturer filed it against 6 model years: 2026 Mercedes-Benz C-Class, 2025 Mercedes-Benz C-Class, 2026 Mercedes-Benz GLC-Class, 2025 Mercedes-Benz GLC-Class, 2024 Mercedes-Benz AMG C63 S E, 2024 Mercedes-Benz AMG C63 S E 4MATIC+. Whether one particular vehicle is affected is a matter of its VIN and its build, not its model year alone.