Mercedes-Benz bulletin LI20.20-P-079938
What it saysComplaint Warning message "Performance limited" in the instrument cluster and vehicle has lack of acceleration. NHTSA’s full summary ↓
Mercedes-Benz filed this with NHTSA as a service bulletin dated Dec 20, 2025, received Dec 24, 2025, about the power train. It names 4 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 Warning message "Performance limited" in the instrument cluster and vehicle has lack of acceleration. Cause - A too high Temp difference between M43/1 Pump Temp Sensor and Temp Sensor in Power Electronics. DTC P0A9300 is detected by too low flow rate in the low temperature circuit of the power electronics N147. - Possible Restriction in the low Temp coolant circuit NT1. The difference between the temperature sensors in the pump from low temperature circuit and in the power electronics are to big. If the difference is too big, DTC P0A9300 will be set in the power electronics. Remedy If DTC P0A9300 is present in N147: • Follow the guided test step for DTC P0A9300 in power electronics N147 • Ensure that all HV safety guidelines are being followed as per WIS and that the vehicle is powered down. • Replace Cooler low temperature LT1 (from cooling circuit of power electronics) • Replace oil cooler (which is mounted on the drive unit) • Replace the complete cooling fluid (G40) from all cooling circuits If DTC P0A9300 is not present in N147: • upload HV CUL (N147 CUL) to paperless • Open TIPS case and attach QT, HV CUL to the case
Document filed under this number
| Document | Kind | Dated | NHTSA id | At NHTSA |
|---|---|---|---|---|
| LI20.20-P-079938 | Service bulletin | Dec 20, 2025 | 11026828 | PDF, 36 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 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 4 model years this bulletin names have filed 149 complaints with NHTSA since 2015. 4 of them name Power Train — 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.
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 power train
Source: same model, same component group34 other manufacturer communications filed against these Mercedes-Benz models under the same component group (power train), newest first. The eight newest are listed; the rest are on the Mercedes-Benz list.
| Number | Kind | Dated | NHTSA’s summary |
|---|---|---|---|
| LI27.00-P-073124 | Service bulletin | Sep 26, 2026 | Complaint Customer complaints relating to automatic transmission 725.0 (NAG3 Classic /9G‑TRONIC automatic transmission) and 725.1… |
| NCU - 2026080002 | Service campaign | Sep 25, 2026 | Mercedes-Benz AG, the manufacturer of Mercedes-Benz vehicles, has determined that on certain subject vehicles, the transmission control unit… |
| LI35.31-P-080353 | Service bulletin | Sep 14, 2026 | Complaint Whining / humming noises (described as foghorn‑like) from the drivetrain in the rear axle area during cornering. (figure 1) On the… |
| LI27.10-P-075869 | Service bulletin | Sep 14, 2026 | Complaint Only vehicles with a variable transfer case are affected. This can be identified through control unit N45 or N15/7 in the quick te… |
| LI 27.10-P-080851 | Service bulletin | Aug 29, 2026 | Complaint Intermittent shift feel or thud/clunk noise perceived, such as a brief jerk or transmission reaction during certain driving situat… |
| LI27.00-P-075630 | Service bulletin | Aug 5, 2026 | Complaint This document is intended as a pre-case diagnostic reference for transmission related concerns. It will also ensure that if a case… |
| LI27.00-P-080840 | Service bulletin | Aug 4, 2026 | Complaint Mercedes-Benz USA is currently experiencing limited availability of transmission fluid specification ATF 236.17 due to a global su… |
| LI33.30-P-080490 | Service bulletin | Aug 3, 2026 | Complaint Leakage/oil leakage at drive pinion sealing ring (input shaft) (Figures 1-2) Minor leakage/slight seepage at coupling flange nut a… |
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 LI20.20-P-079938 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 LI20.20-P-079938 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 LI20.20-P-079938 cover?
The manufacturer filed it against 4 model years: 2026 Mercedes-Benz GLC-Class, 2025 Mercedes-Benz GLC-Class, 2025 Mercedes-Benz GLE-Class, 2024 Mercedes-Benz GLE-Class. Whether one particular vehicle is affected is a matter of its VIN and its build, not its model year alone.