2020 Mercedes-Benz GLS 450: sudden loss of power

Filed Feb 23, 2026 · Electrical, Engine · TN

The vehicle is experiencing deterioration of the main engine wiring harness insulation, resulting in exposed wires contacting each other. This condition has caused intermittent check engine lights and electrical fault codes. The dealership has confirmed that the wiring insulation has degraded, allowing wires to contact each other. The issue appears related to material durability of the harness rather than external damage. The concern is that continued deterioration could result in: •Sudden engine misfire •Loss of power while driving •Engine stalling •Potential electrical short circuit An unexpected loss of engine power at highway speeds could increase the risk of a crash. The dealership indicated that similar harness insulation concerns have been observed on other M256-equipped vehicles. This appears to be a potential safety-related defect involving engine wiring insulation durability.

Filed Jan 31, 2025 · Engine · PA

On a long road trip - about halfway on [XXX] - received an error message on 48v system malfunction - immediately called nearest Mercedes dealership (Richmond Va) to schedule a service - while on the line received an engine overheating pull over and shut it off message - at this point vehicle deaccelerated over riding my control of vehicle speed. Had to navigate from far left lane to right hand emergency lane at 40 mph - very dangerous maneuver as losing power. Vehicle was towed and received a 48v software update - software that deaccelerates the vehicle with no override for safety is a real problem INFORMATION REDACTED PURSUANT TO THE FREEDOM OF INFORMATION ACT (FOIA), 5 U.S.C. 552(B)(6)

Filed Sep 23, 2022 · Electrical, Engine · CA

This incident occurred around 5:50pm on Wednesday, September 21, 2022. I was driving on a merge connector between two freeways in San Francisco at about 60mph, when the vehicle threw a series of error codes and warnings on its displays, culminating with “shut down engine immediately”. The first error was a 48V battery system charging failure, and the second was a warning that coolant was too hot. The instrument panel and steering and brakes did not lose power, but the accelerator no longer worked, and the vehicle slowed down to about 35mph. I had to merge across 4-5 lanes of rush hour traffic at this speed (sketchy) to make it to the side of the freeway, and was able to exit safely and stop in a safe spot. Upon turning off the vehicle for a few minutes and then restarting it, a generic check engine light remained on afterwards. I had the vehicle towed to a Mercedes dealer where the fault(s) are currently being diagnosed. According to the dealer, they are in touch with MBUSA Engineering due to the nature of the fault codes. The vehicle had recently undergone a 50,000 mile routine service without any problems being flagged. The safety implications of this incident are clear: with no ability to match the speed of the flow of traffic, I could have been rear-ended or involved in a collision as I limped across the freeway to safety. I am fortunate that the vehicle had enough residual kinetic energy that I didn’t end up stuck blocking a freeway lane in rush hour traffic. Searching online for similar issues, this appears to be a known manufacturing issue with the mild hybrid inline-6 engine in this model of vehicle. For instance, all of the top Google hits for the term “GLS 48V battery failure” yield relevant and similar reports from other drivers, including summaries from consumer lawyers like this one: https://lemberglaw.com/mercedes-benz-gle-battery-electric-problems/

Filed Mar 14, 2021 · Electrical, Engine · 4,200 miles · HI

We purchased a new 2020 mercedes benz gls 450 in october 2019 from the oakland dealership and shipped the car to hawaii. The vehicle is now 117 months old and has about 4100 miles. Because our vehicle is lightly used we arranged for mercedes benz to supply and installed a 'battery minder' to keep the vehicles 48 volt system charged when we are away for an extended time. However we did not have the battery minder hooked up at this time because we are using the vehicle on a weekly basis. On march 7, 2021 we experienced a "48 volt battery malfunction' which left our car disabled on the side of an uphill major roadway. There was no warning just a sudden extreme loss of power, supplemental systems such as the AC deactivated, warning lights flashed and our vehicle coasted to the side of the road. I believe the brake system was also diminished by the loss of electrical boost. After a while we were able to restart the vehicle and began to 'limp home'. The vehicle was not able to accelerate and we experienced 'over heating' warnings ( in red ) and had to stop the vehicle to cool the engine. We arranged for mercedes benz roadside assistance to tow the vehicle to the kona mercedes benz service centre the next day. Yellow engine warning lights remained on when the vehicle was placed on the tow vehicle.we have used the kona service centre since it was opened, the team LED by paulette gantala is very capable and they perform excellent work. After several days we learned that the cause of the malfunction was not found and we were told to 'monitor the situation'. I attached the service report which describes the extensive investigative work completed by the kona mercedes service centre. We are very concerned this malfunction is a safety related issue and needs to be escalated. Sudden unexpected loss of power creates extremely dangerous situations.

Filed Aug 6, 2020 · Electrical · 8,900 miles · OH

While driving the vehicle, a series of electrical system warnings were displayed in rapid succession. Shortly thereafter, the vehicle lost power, the engine shut off, and the vehicle began to glide. This incident occurred on a residential street while the vehicle was travelling at 25-30 MPH. The warnings were specific to the 48v electrical system. The vehicle was operable after the incident and it was driven to the dealership. The repair invoice and the warning pictures are attached. The issue was traced to a grounding issue as most of the connections between the electrical system and the vehicle's chassis were inappropriately filled with paint (assumed from the vehicle assembly process).