2019 Mercedes-Benz GLC 300

On January 8, 2021, after ongoing review with Mercedes Benz, the National Highway Traffic Safety Administration (NHTSA) Office of Defects Investigation (ODI) opened PE21-001 to assess allegations of front roof panel detachments while driving at highway speeds in certain 2015 Mercedes-Benz (Mercedes) C-Class vehicles.The subject front roof panel is a stationary panel composed of polycarbonate and is attached to the vehicle via adhesive at the time of manufacture. The panel is found on subject vehicles equipped with panoramic sunroofs. Over time, the subject panels may exhibit cosmetic degradation leading to replacement of the panel, a procedure which entails: removal of the old panel and adhesive, site preparation, and installation of a replacement panel with new adhesive.The consumer complaints that prompted the opening of PE21-001 all described detachments of front roof panels that had been replaced after the vehicle was put into service.Mercedes' internal investigation identified a broader scope of affected vehicles (2014-2020 CLA, GLA, C, S, GLC, and GLE class) and found the following potential service procedure- related causes of front roof panel detachments:- Improper surface pretreatments such as the use of the wrong primer or cleaner or scoring of the surface; or - Use of the incorrect adhesive.These conditions lead to a front roof panel bond that, even if sound at the time of repair, cannot maintain its strength over time and environmental exposure.Mercedes updated its service and parts ordering systems to reinforce the proper use of specified kits and procedures via webinars, shop foreman meetings, and explicit reference to the risks incurred by diverging from the repair procedures. Mercedes is also furnishing parts ordering assistance, and will hold dealerships accountable for improper repairs.ODI's analysis of the ten complaints it has received from the public (VOQ's) and MBUSA's complaint data submitted in response to the information request letter for PE21-001 identified a total of 57 non-duplicative reports alleging incidents in which the front roof panel detached from the vehicle while in motion. Included within the 57 reports are incidents where consumers state the panel detached ...and flew off into traffic.On March 19, 2021, Mercedes notified NHTSA that it would recall subject vehicles with front roof panels known to have been replaced after the original sale of the vehicle. In total, the recall (designated as Recall 21V197) covers 15,099 vehicles that were ever registered in the United States. Based on Recall 21V197 and the remedy implemented by Mercedes, further investigation does not appear to be warranted at this time.Accordingly, this investigation is closed.The ODI complaints cited above can be viewed at www.nhtsa.gov under the following ODI identification numbers: 11376425, 11352686, 11351629, 11349158, 11341541, 11337594, 11324100, 11311591, 11222127, 11404183

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 NHTSA 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.

NHTSA ID

11736351

Incident

Apr 16, 2026

The contact owns a 2019 Mercedes-Benz GLC300. The contact stated that while driving 65 MPH on the interstate, the sunroof suddenly shattered into pieces and flew off the vehicle. The vehicle was driven to a dealer but was not repaired. The manufacturer was notified of the failure. The failure mileage was 106,706.

NHTSA ID

11729435

Incident

Apr 5, 2026

Mileage

106,706 mi

I have a MC Benz 300 GLC with $50,000 miles. I was having heating issues so took it to the dealership, which basically advised of the issue describer below, which would cost $14k to repair. Contaminated coolant in Mercedes-Benz GLC 300 models often results from the internal failure of a "desiccant bag" inside the coolant expansion tank, which disintegrates, releasing material that clogs the heater core. Symptoms include black residue in the tank, reduced cabin heat, and engine overheating. Key actions include replacing the expansion tank (reservoir) and flushing the entire system.

NHTSA ID

11728476

Incident

Mar 31, 2026

A message that passenger air bag is damaged/will not deploy appears. Passenger seat belt gets stuck and cannot be opened. Check engine light on-pvc valve issue most likely.

NHTSA ID

11726943

Incident

May 1, 2025

SUNROOF EXPLODED AND SHATTERED. I HEARD IT WHILE DRIVING AND HELD ON TIGHTLY TO THE STEERING WHEEL BEFORE I REALIZED WHAT IT WAS. THE DEALER AND MY AUTO INSURANCE HAVE BEEN CALLED, NEITHER PICKED UP, AND I LEFT EACH A VOICE MAIL MESSAGE. NO WARNING LAMPS, MESSAGES OR OTHER SYMPTOMS OF THE PROBLEM OCCURRED.

NHTSA ID

11721035

Incident

Feb 27, 2026

My sunroof just exploded while driving on the highway without any impact or warning. It was a clear sunny day. There wasn't a vehicle in front of me. Nothing fell on my windshield nor sunroof. The sudden explosion and shattering of the glass was extremely startling. I had a mesh underneath the sunroof that contained some of the shattered glass so it did not fall on me while I was driving. I'm so thankful there wasn't a car behind me for the glass debris to fall on. Mercedes USA was not helpful, unresponsive for many weeks. They eventually declined repair coverage due to out of warranty, not manufacture defect nor safety issue.

NHTSA ID

11716844

Incident

Dec 30, 2025

I was driving on a street 5mph and all of a sudden my car surged and led me to curb where i knocked hit a steer din and it veered onto someone’s lawn and hit a huge planter and stopped . Air bags were deployed . I had no control over the car . EDR was preformed and I’m sure it was a throttle surge issue and cause unintended acceleration . The edr shows I was going 5 miles an hour but then says pedal was pushed to 100%. While traveling at approximately 4–5 mph during a low-speed maneuver, with light accelerator input, the vehicle unexpectedly surged forward. I did not intend to accelerate. The vehicle rapidly increased speed, left the roadway, struck a street sign and a planter, and the airbags deployed. Event Data Recorder (EDR) data retrieved by the insurer (Mercury Insurance) shows the vehicle traveling at low speed immediately prior to the event, followed by a recorded 100% accelerator pedal position. This data does not reflect my driving intent and appears inconsistent with the low-speed conditions. The EDR documentation notes that accelerator pedal position is sampled asynchronously and reflects values transmitted to the SRS Control Module, not continuous pedal input or driver intent. No brake input was recorded prior to the impact. The sudden acceleration occurred too quickly to react. Mercedes-Benz inspected the vehicle and released only the EDR data, declining to provide further clarification regarding throttle control logic, pedal sensor correlation, or torque command behavior. I am reporting this incident due to concern that low-speed throttle control behavior, software logic, or transmission engagement may result in unintended acceleration without corresponding driver intent, posing a safety risk during parking-lot or low-speed driving conditions.

NHTSA ID

11714225

Incident

Aug 11, 2025

The contact owns a 2019 Mercedes-Benz GLC300. The contact stated that while shifting from reverse to drive, the vehicle stalled and remained in neutral. After the vehicle stalled, the vehicle took approximately 8 minutes before the vehicle could be shifted into drive. Once in drive, the vehicle would jerk and shift to D3 before accelerating. The check engine warning light would illuminate while in reverse. The vehicle was taken to the dealer, who diagnosed a transmission failure due to a malfunctioning valve body and low pump pressure. The dealer confirmed that the VIN was not under recall and that the issue was not covered under warranty. The vehicle was not repaired. The contact informed the manufacturer of the failure, and a case was opened. The manufacturer referred the contact to the NHTSA Hotline to report the failure. The failure mileage was approximately 60,000.

NHTSA ID

11700738

Incident

May 21, 2025

Mileage

60,000 mi

This NCU replaces the prior NCU issued on May 15, 2025, and contains additional MY 2023 and MY 2024 vehicles which are highlighted below. In our continuing efforts to ensure the proper performance of Mercedes-Benz products and to enhance the satisfaction of our customers, Mercedes-Benz USA, LLC (“MBUSA”) is extending the warranty coverage on the Diagnostic Module for Tank Leakage detection (DMTL) in certain Model Year (“MY”) vehicles listed below from the original New Vehicle Limited Warranty of 4 years/50,000 miles to 10 years/120,000 miles (vehicles certified as LEV II) and 15 years/150,000 miles (vehicles certified as LEV III), whichever occurs first, for the following condition: •Under certain circumstances, the DMTL may trigger erroneous Diagnostic Trouble Code (DTC) entries that may result in the illumination of the Check Engine Malfunction Indicator Lamp (‘MIL’).

Mercedes-Benz AG (“MBAG”), the manufacturer of Mercedes-Benz, has determined that on certain MY 2019-2021 C-Class, G-Class, GLC, GT, S-Class (205, 463, 253, 190 & 222 platforms) vehicles, the engine control unit software does not correspond to current production specifications. It is therefore possible that on-board diagnostics and/or exhaust gas emissions requirements may not be fulfilled.

Single throttle lift-off clunking noise from the side shaft when moving off (audible at the outboard end). The noise is heard once in each instance when changing direction of travel. Note: Sound file in attachment Cause If the complaint is eliminated by experimentally loosening the outboard collar nut (by 1 turn), the problem is due to cracking of the microweld between the wheel bearing inner race and the joint housing of the side shaft. Note: The collar nut must always be replaced after being loosened. See also LI33.20-P-078406 Remedy Coat contact surface of side shaft with wheel bearing with Molykote paint. To do this, proceed as follows: 1. Remove side shafts 2. Clean contact surface A (see image file in attachment "Outer joint housing before") before coating with Molykote, using "spirit" (free of dust and grease) 3. Coat contact surface A (see image file in attachment "Outer joint housing after") with Molykote and leave to dry for "one hour" in removed condition 4. Reinstall side shafts Note: Before using the antifriction coating (Molykote), stir it or shake it thoroughly for (at least 1 minute).

Complaint Creaking noise, in irregular sequence when driving slowly in combination with slight steering movements and/or Creaking/crackling noises from the area of the wheel bearing on the front axle when cornering/ maneuvering. Sound file attached for comparison. MUST match noise for proper diagnosis. NOTE: Steering functionality is not affected. Cause Contact area between wheel bearing and steering knuckle. See also: LI35.30-P-058566 (Throttle Lift-Off Noise - Rear) LI33.30-P-056665 (Throttle Lift-Off Noise - Front) LI40.10-P-059248 (Wheel cracking noise when cornering) Remedy 1. Perform Operation A and evaluate by testing vehicle. 2. If noise is still present after re-testing: • If 192/232 chassis, verify FIN is in the listed range below in "Operation B" and perform. • If not 192/232 chassis or vehicle is a 192/232 not in the listed FIN range, additional verifications of where the noise is coming from are needed. Use multiple channel NVH method to narrow down location. Verify the LI's listed above were completed or if there are other similar noises associated with the chassis (Example: 192/232 also has under panel noises and an associated LI). Operation A: 1. Clean contact surfaces of wheel bearing and steering knuckle with brake cleaner as seen in the attached pictures. NOTE: The front area of the wheel bearing and the seals must not come into contact with the cleaner, otherwise, the sealing rings will be damaged. 2. Clean threads of wheel bearing mounting. 3. Thinly coat contact surfaces of wheel bearing, steering knuckle, and axle mating face with Molykote (annular joint grease). See the attached steering knuckle and wheel hub pictures for reference. NOTE: Axle mating face greasing is also covered in LI35.30-P-058566 and LI33.30-P-056665. Operation B (Only applies to 192 and 232 in listed FIN range): Only affects vehicles up to FIN end number: • Model series 192: xxx xxx xx 002 876 • Model series 232: xxx xxx xx 022 312 1. Replace steering knuckle. 2. Wheel bearings do not need to be replaced.

Complaint Creaking noise, in irregular sequence when driving slowly in combination with slight steering movements and/or Creaking/crackling noises from the area of the wheel bearing on the front axle when cornering/ maneuvering. Sound file attached for comparison. MUST match noise for proper diagnosis. NOTE: Steering functionality is not affected. Cause Contact area between wheel bearing and steering knuckle. See also: LI35.30-P-058566 (Throttle Lift-Off Noise - Rear) LI33.30-P-056665 (Throttle Lift-Off Noise - Front) LI40.10-P-059248 (Wheel cracking noise when cornering) Remedy 1. Perform Operation A and evaluate by testing vehicle. 2. If noise is still present after re-testing: • If 192/232 chassis, verify FIN is in the listed range below in "Operation B" and perform. • If not 192/232 chassis or vehicle is a 192/232 not in the listed FIN range, additional verifications of where the noise is coming from are needed. Use multiple channel NVH method to narrow down location. Verify the LI's listed above were completed or if there are other similar noises associated with the chassis (Example: 192/232 also has under panel noises and an associated LI). Operation A: 1. Clean contact surfaces of wheel bearing and steering knuckle with brake cleaner (see areas marked blue in pictures "2.jpg" and "3.jpg"). NOTE: The front area of the wheel bearing and the seals must not come into contact with the cleaner, otherwise, the sealing rings will be damaged. 2. Clean threads of wheel bearing mounting. 3. Thinly coat contact surfaces of wheel bearing, steering knuckle, and axle mating face with Molykote (annular joint grease) (see areas marked blue in pictures "2.jpg" and "3.jpg"). NOTE: Axle mating face greasing is also covered in LI35.30-P-058566 and LI33.30-P-056665. Operation B (Only applies to 192 and 232 in listed FIN range): Only affects vehicles up to FIN end number: • Model series 192: xxx xxx xx 002 876 • Model series 232: xxx xxx xx 022 312 1. Replace steering knuckle. 2. Wheel bearings do not need to be replaced.

Dear Mercedes-Benz USA Dealers, The part numbers listed in the chart below should no longer be installed, and any existing stock must be returned to your facing PDC. The deadline for all dealer returns is no later than Thursday, July 9, 2026. After July 9th, returns of these parts will no longer be accepted. These parts should be returned via ZSR Special Return, using item category SCM Authorized Part Return. Please include a copy of this NCU as your authorization to return these parts. This procedure will not affect your return allowance. All returned parts will be replaced in accordance with the chart provided below.