2020 Mercedes-Benz GLS 450: check engine light

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 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 May 17, 2022 · Electrical, Engine · AZ

While driving, vehicle has abruptly stopped/engine turned off causing car to not accelerate and come to a stop. One instance was on a busy freeway, causing our family to pull off the interstate with nearly no curb, risking rear-end collision due to the abrupt stalling of the vehicle. In this instance, the 48 volt battery failure warning, engine overheat warning, engine light warning came on. When MCB dealership evaluated the vehicle, there were no stored associated error codes and MCB service returned the vehicle to me saying that the issue did not occur when they drove it. The same issue occurred again 5 months later, this time in a busy intersection, where the car would not accelerate and I was forced to pull of the road. The check engine light as well as other failure lights came on. THe car was returned to MCB service and again, no error codes were stored and the dealership said they could not find the cause of the problem. This vehicle issue (reported to the federal safety agency by several other 2020 GLS owners) is a LIFE-THREATENING DANGEROUS VEHICLE PROBLEM . Both times, the engine abruptly failed and the car would not accelerate in the middle of heavily trafficked roads/freeways, which could easily result in a catastrophic accident. Both times, the vehicle did not store the associated error codes, despite the display illuminating several warning lights, including the check engine light. THe unreliability of this expensive vehicle is particularly concerning to me as it is used to transport young children. Mercedes is taking no accountability for this vehicle failure and claims they have not heard of this issue prior, which is clearly inaccurate given that it has been reported to the federal safety agency by several other GLS owners. This is an enormous safety liability, not only for the owners of this vehicle, but for innocent bystander drivers who could easily have a rear end collision with the car as it fails to accelerate and the engine abruptly stalls/stops.

Filed Oct 5, 2021 · Electrical · MI

Upon starting the car, the screen of the 2020 Mercedes Benz GLS 450 remained blank. This includes the portion of the dashboard that reads speedometer, gas, temperature, RPM. The engine was running and truck could still be driven. The vehicle is available for inspection upon request. This is a major safety issue as the driver does not have visibility to the dashboard with all it's important information. The vehicle is currently at Mercedes Benz dealership undergoing diagnostics. The vehicle is being inspected by Mercedes Benz (manufacturer). See prior comment. There were no warning lamps or messages that appeared prior to the problem. Shortly after driving home (with the blank screen) the car was shut off and restarted and the display came back on but then the check engine light was displayed.

Filed Aug 5, 2021 · Fuel system, Steering · CA

We were driving the vehicle at about 30 MPH on a road when suddenly the engine completely shut off. There was no more power steering and no warning that it turned off. We got the car slowed down and once we came to a stop the car put itself in Park. After that we could restart it and keep driving with the car acting very different. This then happened again later on in the day going about 20 MPH up to a stop light. It shut itself off and luckily we were able to come to a stop with the brakes without running into the intersection and no one hitting us from behind. Once again it put itself in Park. We were able to restart the car and drive again with diminished power and really weird shifting from the transmission. The check engine light turned on both times and when we got it to the dealership the next morning all the check engine lights were off again. This is extremely dangerous to the driver and occupants. Our little son was in the back seat. We commute with this car in southern california and if this were to happen on the freeway it would be disastrous. Everyone is at risk with this car. It will just stop without any warning signs and you can have someone rear end you. And the power steering turns off also which if the car turns off in a corner on the freeway you will have no way of controlling the vehicle and will just go into the middle barrier or oncoming traffic. This could be even worse if driven on a mountain road and you loose all power of the vehicle. We will not be driving the car anymore since we have no idea when it will shut off again while driving.

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.