Mercedes-Benz GLC 300 loss of power problems

Filed Oct 26, 2026 · Electrical, Engine · MD

On October 23, 2026, my 2020 Mercedes-Benz GLC 300 unexpectedly lost engine power while I was in traffic, without advance warning. When I attempted to restart it, the engine started, shook, and shut off again. A 12-volt battery warning appeared during the incident. On October 26, a dealership representative told me a software issue caused the shutdown and that a software update was needed. They said the update would be performed at no charge, although I would owe a diagnostic fee. I am concerned that the vehicle could lose power without warning again, especially at highway speeds. I am requesting that the federal safety agency review this incident for a possible safety defect.

Filed Oct 1, 2026 · Fuel system · GA

The vehicle has experienced two separate incidents of significant loss of power/acceleration. First incident – January 2024, Clarksville, TN: While driving downtown, the vehicle suddenly lost significant power and could not provide normal acceleration. The estimated remaining range was approximately 50 miles. The vehicle was subsequently inspected/serviced by Mercedes-Benz/dealer personnel, but the underlying cause was not conclusively identified or resolved. Second incident- [XXX] [XXX]: While driving in the first lane of [XXX], the vehicle suddenly lost significant power/acceleration when the estimated remaining range was approximately 75 miles. There were no warning alarms or messages before the loss of power. My wife and child were in the vehicle. The vehicle could not provide normal acceleration in highway traffic, creating an extremely dangerous situation. The incident nearly resulted in a serious traffic accident, and my wife had to take immediate action to help avoid a potential collision. The vehicle was subsequently inspected by Mercedes-Benz/dealer personnel, but the specific loss-of-power condition was not conclusively reproduced or confirmed under the circumstances in which it occurred, and the underlying cause was not identified or resolved. The vehicle has therefore experienced this type of serious power-loss condition twice despite service attempts. I can no longer safely drive or intentionally test the vehicle to reproduce this condition. Attempting to drive until approximately 75 miles of remaining range could cause another sudden loss of power and potentially result in a serious accident. I will not intentionally recreate a potentially dangerous failure on a public highway with my family or other motorists at risk. I am reporting this because unexpected loss of power while traveling on a highway presents a serious safety hazard and potential collision risk. INFORMATION REDACTED PURSUANT TO THE FREEDOM OF INFORMATION ACT (FOIA), 5 U.S.C. 552(B)(6)

Filed May 27, 2026 · Transmission · CA

While driving my 2024 Mercedes-Benz GLC 300 on California highways, the vehicle has repeatedly experienced sudden uncontrolled deceleration, unexpected transmission downshifts into 2nd gear, severe transmission jerking, and complete loss of accelerator response. The first major incident occurred on March 7, 2025, while traveling on Interstate 5 at approximately 70 mph. The transmission suddenly jolted and downshifted directly into 2nd gear. The vehicle immediately lost power and slowed to approximately 20 mph without warning. I exited the highway and restarted the vehicle before it temporarily resumed normal operation. A second major incident occurred on May 7, 2026, while driving on Interstate 5 near Flag City, California at approximately 65 mph. The vehicle suddenly decelerated uncontrollably to approximately 20 mph. The transmission again shifted directly into 2nd gear, and the accelerator pedal became completely unresponsive. I was forced to make an emergency stop on the shoulder of the freeway with hazard lights activated due to the risk of being rear-ended by high-speed traffic and trucks. A third incident occurred on May 13, 2026, while accelerating onto Highway 99 in Modesto, California. During a shift from 4th to 5th gear, the transmission jerked violently and the vehicle suddenly lost power while merging into highway traffic. The vehicle has been taken to Mercedes-Benz of Stockton multiple times for diagnosis and repair attempts. The dealership has performed software updates and extensive testing, and dealership personnel have personally verified the transmission defect during road testing. Mercedes-Benz engineering has also become involved in the diagnosis process. However, the defect remains unresolved. This defect creates a serious highway safety hazard due to sudden loss of propulsion, uncontrolled deceleration, and loss of accelerator response while driving at freeway speeds.

Filed May 20, 2026 · Engine · AL

While driving in my neighborhood at 25 MPH, my Mercedes GLC300 suddenly lost power and the check engine light illuminated. My car would no longer exceed 25-30 MPH, but I drove it straight to the dealership and they said it was a faulty cylinder head and will cost $10,000 to fix! After intense negotiations, they agreed to fix it for $4,205.58, which was better, but still, that’s a lot to pay for a manufacturer’s defect! My car is a 2021 with only 67,540 miles on it.

Filed May 7, 2026 · Electrical, Transmission · NY

On April 16, 2026, within minutes of being released from a certified dealership, my 2019 Mercedes-Benz GLC 300 suffered a sudden and total loss of propulsion while traveling at high speed on the Belt Parkway (NY). Despite depressing the accelerator, the vehicle failed to maintain speed and stalled in active traffic. This created an immediate life-safety hazard, forcing me to navigate across multiple lanes without engine power to avoid a high-speed rear-end collision. The vehicle was released to me by Mercedes-Benz of Brooklyn on April 16, 2026, following a repair for which I paid $2,134.94. The dealership diagnosed the issue as a wiring harness/sensor fault and formally certified the vehicle as "Found OK" and safe for operation. The catastrophic failure occurred only 22 minutes after I departed the dealership lot. The vehicle had to be towed back to the facility immediately. Upon the vehicle being towed back on April 16, the dealership admitted via recorded voicemail that the initial $2,134.94 repair was a misdiagnosis. They subsequently issued a new diagnosis for a "Valve Body" failure and a new quote of $6,424. The dealership's Service Director has since admitted the vehicle suffers from concurrent transmission and engine failures, rendering the car a liability. This represents a critical failure of the powertrain and electronic control systems. Releasing a vehicle that suffers a total power loss on a highway immediately after a "certified" repair is gross negligence. I am reporting this to the federal safety agency as a catastrophic failure of a safety-critical component (Transmission/Valve Body) that resulted in a "dead-stick" situation on a major New York thoroughfare, posing a severe risk to myself and other motorists. The vehicle remains at the dealership. Mercedes-Benz USA has offered only a $2,000 "goodwill credit," which does not address the safety defects or the initial misdiagnosis. No recall has been initiated for this batch.

Filed Mar 2, 2026 · Fuel system · TX

The contact owns a 2022 Mercedes-Benz GLC300. The contact stated that while driving at various speeds and depressing the accelerator pedal, the check engine warning light was displayed on the instrument panel. The vehicle lost power and was pulled over and restarted. The contact was almost involved in several crashes due to the failure. The vehicle was included in the federal safety agency Campaign Number: 23V445000 (Fuel System, Gasoline); however, the vehicle was repaired, and the failure persisted. The vehicle was taken to the dealer on several occasions, where the fuel pump, charcoal filter, and other various parts of the fuel pump were repaired; however, the failure persisted. The manufacturer was notified of the failure, and the contact was informed that the cylinder head would be replaced free of charge. The contact believed that the vehicle was unsafe to drive due to the failures. The vehicle was not repaired, and a loaner vehicle was provided. The failure mileage was unknown.

Filed Jan 8, 2026 · Engine, Transmission · CA

Vehicle Information: Year: 2021 Make: Mercedes-Benz Model: GLC 300 Engine: M264 Mileage at time of failure: Approximately 65,000 miles Complaint Description: While driving, my 2021 Mercedes-Benz GLC 300 began experiencing repeated engine misfires and rough running, accompanied by a persistent check engine light. These symptoms began shortly after I purchased the vehicle and progressively worsened over time. The vehicle exhibited reduced engine performance and hesitation while driving. The condition was intermittent at first but became more frequent, indicating a progressive mechanical issue rather than a sudden failure. At approximately 65,000 miles, the vehicle was evaluated by an authorized Mercedes-Benz dealership and diagnosed with a catastrophic cylinder head failure, requiring full cylinder head replacement. The estimated repair cost is approximately $8,000. The vehicle has never been modified and has not undergone prior engine repairs. The failure occurred well before what would be considered normal wear for an engine component of this type. Based on the progression of symptoms, the dealer diagnosis, and similar reports from other owners of the same model and engine, this appears to be a systemic defect involving the cylinder head and valve train, rather than an isolated incident or maintenance-related issue. This condition presents a potential safety concern due to loss of engine performance, drivability issues, and the risk of reduced power while operating the vehicle.

Filed Dec 30, 2025 · Engine · NJ

While I was driving on the Garden State Parkway, my vehicle experienced a sudden loss of power and persistent misfires and my check engine light came on. I was put in a position of a significant crash risk due to the fact that the vehicle loss sudden acceleration power while entering the parkway. I was almost rear ended by another vehicle. I drove immediately to a Mercedes-Benz dealer. The dealer confirmed a catastrophic cylinder head engine failure. The vehicle had only 39,000 miles. After some investigating, there have been numerous complaints from vehicle owners with the same issue on the M264 engine (which is what my vehicle has). I request that the federal safety agency investigate the premature cylinder head engine failure. Not only was I put at risk for a possible significant accident, the manufacturer has refused to consider some reimbursement for my $10,000 repair. The vehicle was only 3,000 miles out of warranty at the time of the engine failure. A safety issue seems to be warranted and possibly a recall because of the many complaints on the GLC website. Please investigate.

Filed Dec 8, 2025 · Engine · CT

The engine in my 2020 Mercedes-Benz GLC 300 suddenly malfunctioned while driving on two separate occasions. The vehicle began shaking violently and lost power without warning. I could not accelerate and had to pull over immediately. I turned the vehicle off and restarted it to regain limited driveability. On the second incident, the power loss was so abrupt that it felt as if I had been rear-ended. I feared the vehicle would stall in traffic and cause a crash. Following these events, the check engine light remains constantly on. The dealer inspected the vehicle and confirmed excessive valve leakage into the exhaust system, requiring a complete cylinder-head replacement. They warned the failure will worsen and could result in sudden power loss again. This defect poses a serious safety risk. If the power loss occurs while merging or at highway speeds, it could easily lead to a rear-end collision. The vehicle has relatively low mileage for such a severe internal engine failure, and I have learned that other owners of this same engine have reported similar issues. Sudden stalling or loss of acceleration places occupants and other drivers in danger. There were no warning messages prior to the failure, and the problem has recurred. The vehicle is available for inspection, and the defect has been confirmed by a Mercedes-Benz service center. This appears to be a mechanical defect in the engine design, potentially involving valve seat failure. An investigation is needed to determine if this issue is widespread and whether a recall or manufacturer action is required to prevent accidents or injuries.

Filed Nov 3, 2025 · Fuel system · FL

The vehicle lost power and will not operate over 40 mph/2000 rpms