NHTSA Complaint #11668223 — 2021 MERCEDES-BENZ GLB 250

In April 2025, my 2021 Mercedes-Benz GLB 250 (81,000 miles) suffered repeated engine issues caused by a cylinder head failure. The dealer attempted a cylinder head replacement, but during their own test drive after repairs, the engine completely seized and failed again on their property. This indicates a severe defect in the engine assembly that risks sudden power loss while driving, which could cause an accident. Prior to the failure, there were warning messages about misfires and rough idle. The problem has been confirmed by an authorized Mercedes-Benz dealer and the car has been kept at their shop since April, with no resolution. I am concerned this is a recurring safety defect affecting other GLB 250 vehicles. The vehicle is available for inspection and remains undriveable due to the failed engine. I request NHTSA to investigate for possible safety-related design or manufacturing defects that could cause sudden engine seizure and loss of power while driving.