The issue is regarding the “Traffic Sign Assist” (Owner’s Manual page 221) feature of the Adaptive Cruise Control System. Vehicle will be made available if requested. The function of the "Traffic Sign Assist" is to monitor roadside "Speed Limit" signs and the cruise control will increase or decrease speed to stay within the permissible legal speed limit. The system worked except occasionally it would change the indicated permissible speed limit on the instrument display when there is no corresponding roadside speed limit sign and the permissible speed limit for that stretch of roadway is unchanged. When this happens, suddenly and abruptly, the vehicle display would indicate a "phantom" Higher or Lower Speed Limit sign and rapidly and abruptly accelerate or decelerate. Again there were no roadside signs posted indicating a higher or lower speed limit! The risk is potential for rear end collisions from or to other traffic due to the abrupt acceleration or deceleration. when we returned home from a 4556 mile road trip, we took the vehicle to the Mercedes dealer for routine service and mentioned this to the Service Advisor. He indicated that when this defect is reported their solution is to deactivate the system. I don't feel this is adequate since another driver could reactivate the system through the settings. It has not been inspected by anyone except the dealer. There were no warning lamps, messages or other symptoms before the display changed and the vehicle abruptly accelerated or decelerated.

Source: NHTSA complaint ODI #11732594 · view all complaints for this vehicle at nhtsa.gov

The contact owns a 2023 Mercedes-Benz GLC300. The contact stated that while driving at an undisclosed speed, the speed limit warning system failed to function as intended. The contact stated that while driving 60 MPH, the Heads-up Display (HUD) illuminated a red light and an unknown message about driving too slowly was displayed. The contact stated that the red light illuminated and flashed intermittently. The vehicle was taken to the dealer, and the contact was informed that the failure was common with the vehicle. The vehicle was not repaired. The contact stated that the failure persisted. The contact asked if the speed limit warning system could be deactivated, and the dealer was informed that it had to be approved by the manufacturer. The manufacturer was made aware of the failure. The contact was referred to the dealer for assistance. The contact stated that the dealer and the manufacturer offered no assistance. The failure mileage was approximately 12,000.

Source: NHTSA complaint ODI #11725658 · view all complaints for this vehicle at nhtsa.gov

The contact owns a 2023 Mercedes-Benz GLC 300 4MATIC. The contact stated that while driving at an undisclosed speed, the brake pedal was depressed; however, the brake pedal felt as if it had released, and the vehicle failed to stop as needed. The contact stated that the failure was a recurring failure. The dealer was contacted but could not duplicate the failure. The vehicle was not diagnosed or repaired. The manufacturer was not made aware of the failure. The failure mileage was approximately 39,000.

Source: NHTSA complaint ODI #11752677 · view all complaints for this vehicle at nhtsa.gov

This 2023 GLC, a newly redesigned model, has a number of issues. The two most severe are the adaptive speed limit and the lane keeping assist. I had to disable the traffic sign recognition feature because I was on I-95 in Maryland where the posted speed limit was 65. The car abruptly slowed me down to 35 because it saw an exit sign speed limit but I was not on the exit. I was lucky the car behind me didn't hit me. A warning would be good but to brake the vehicle for a speed limit sign seems problematic. The more serious issue is the lane keeping assist. The car is supposed to show green markers when I'm above 37MPH and on a marked road. Normally, one turns red and eases the car back into the lane if I drift. There are 3 settings and mine is set to provide the most warning. If the system works (it sometimes does) I am already on the line at the alert. Typically, it could care less where I am in relation to road markings and will let me drift across lanes with no warning whatsoever. I took the car in to the dealership several times for this. The first time, they said "it's designed so you can't trick it." I didn't buy that. I then took it our for a drive with the service manager. He said "it detected steering input". I then let it drift across the road marking while removing my hands from the wheel and it provided no warning whatsoever (no turn signal use to disable the function). I asked him if he saw steering input that time. He said "I need a video of this". This issue has supposedly been sent to the engineers in Germany but this problem existed when new and it's been weeks with no resolution. This is a backup system but it is something I certainly paid for and would like to know it works should I actually need it. All testing was done in a safe manner and not around traffic. I can only attach pictures but I have videos as well. The dash should not be showing green lane markings on both sides in any of these screenshots from videos.

Source: NHTSA complaint ODI #11538722 · view all complaints for this vehicle at nhtsa.gov

Unknown: Driving on Route I 71 south in Cincinnati going CVG to pick up wife. 60-70 MPH. All systems normal.Suddenly out of blue , Brakes slam on 3-3 seconds seatbelt locks on and car deaccelerates with no warning , no lights , no registered failure. Belt compression severe, almost brushing strength. My wife has a spinal injury, cage in her neck ., must wear brace . She was not driving, tell Chris Walker to have service pick up , take care of open recall, fix sudden development of violent sudden deceleration with Violent seat belt tensioner compression . Really catastrophic Situation. Could have occurred . Glad I was driving . Could have been tragic. 3rd glc300 17-23 ?????????????????????!!!!!!!!!!

Source: NHTSA complaint ODI #11551129 · view all complaints for this vehicle at nhtsa.gov

I purchased a new Mercedes Benz GLC300 2023. Last month, my friend and I were driving on I75 in Florida when we heard what sounded like a loud boom or gunshot. We quickly discovered that my sunroof had exploded. The sunroof was closed, and fortunately so was the sunshade, as large pieces of glass flew off the roof and smaller shards of glass collected on top of the sunshade. My friend and I were fortunate to have not been insured and were able to safely navigate the vehicle to the side of the road to assess the damage. In contacting the MB dealership, I learned that the sunroof is considered "glass" and thus not covered under warranty even though the vehicle is only 3 years old with less than 50,000 miles. What is more concerning to me is that the roof was not under a recall, and there have apparently been other MB owners that have experienced the same issue with class action lawsuits pending. My insurance company covered the repairs following payment for the deductible. This huge safety concern is that we could have been seriously injured by flying and/or falling glass. I write to express my deepest concern over the safety issue the exploding roof presents-the cost of repair relative to what could have happened is minor. Thank you for the attention to this matter.

Source: NHTSA complaint ODI #11733932 · view all complaints for this vehicle at nhtsa.gov