The engine-driven vacuum pump and turbocharger boost-control vacuum system malfunctioned. The vehicle developed insufficient vacuum to the boost-control system, resulting in a P0299 turbocharger underboost fault and reduced engine power. The vehicle is available for inspection upon request. The vehicle experienced a noticeable loss of peak power and reduced acceleration. Although it did not enter limp mode, unexpected reduced acceleration could create a safety risk while merging onto a highway, passing another vehicle, entering or crossing traffic, or attempting to avoid a collision. An authorized Mercedes-Benz dealership scanned the vehicle, confirmed fault code P0299, and documented that vacuum supplied to the turbocharger boost-control system was too low. The dealership recommended replacing the vacuum pump and retesting the vehicle. The vehicle was inspected and diagnosed by an authorized Mercedes-Benz dealership. Mercedes-Benz USA reviewed the case and the dealership’s diagnosis as part of a goodwill-assistance request, but Mercedes-Benz USA did not physically inspect the vehicle. The vehicle has not been inspected by police or insurance representatives. The check-engine light illuminated, and the vehicle stored a P0299 turbocharger underboost fault. I also noticed reduced peak engine power and weaker acceleration. The vehicle did not enter limp mode. These symptoms first appeared at approximately 42,000 miles on or around June of 2026. Mercedes-Benz has issued an extended warranty for vacuum-pump failures on certain M157-powered vehicles that identifies the same vacuum-pump part number used in my M276-powered GLC 43 and describes similar symptoms, including low boost, a check-engine light, and P0299. Although my vehicle is not currently included in that extension, the use of the identical component and substantially similar failure raises concern that the affected population may extend beyond the listed M157 models.
NHTSA ODI 11747935