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What 14 owners told NHTSA about the 2021 Mercedes-benz C-class Phev

These are the actual owner complaints behind this car’s reliability verdict, filed with the federal government, unedited. They’re unverified reports, not confirmed defects: read them as leads for your pre-purchase inspection, not a diagnosis.

All (14)Engine (7)Fuel system (3)Airbags (2)Transmission & drivetrain (2)Backup camera & sensors (1)Electrical system (1)Suspension (1)Visibility & wipers (1)

2 of 14 complaints match · Transmission & drivetrain · clear filters

Dec 9, 2025SuspensionTransmission & drivetrainAirbags

Driving and something came from underneath the vehicle and cause me to swerve in all the airbags deployed

NHTSA ODI 11704073

Aug 6, 2025Transmission & drivetrainEngine

My C300 only had about 42,000 miles and was less than 5 years old. Just after the factory warranty expired, the engine was running rough and hot, and "check engine" light illuminated. My local garage quickly diagnosed the problem as a failed cylinder head, stated that it is common with Mercedes 4-cylinder engines from about 2017, and said Mercedes may cover it since it is a "known problem" and shouldn't happen with that mileage. I was charged $7,860 by my local Mercedes dealer, and despite multiple contacts with MercedezUSA, they refuse to acknowledge this is a problem or cover the cost, although in on-line the forums some people were arbitrarily reimbursed. There should be a recall to check for this obvious defect and should be covered. This defect can cause sudden engine failure and is a significant hazard to the driving public.

NHTSA ODI 11678865

Working with the data? Download all 14 complaints as CSV · fetched from NHTSA July 21, 2026

How to use these: a complaint is one owner’s report, filed voluntarily and published unverified. Patterns matter more than any single story. If several owners describe the same failure at similar mileage, put that system at the top of your pre-purchase inspection list. Back to the full 2021 Mercedes-benz C-class Phev verdict →