2018 Mercedes-Benz C-Class Reliability Report

The most serious pattern is a transmission that shifts itself into neutral while driving and will not go back into drive. Dealers blame a failed transmission control unit, valve body, pressure control valve, or shifter module, and one valve body repair was quoted at $3,800. Two crash reports involve the car lunging forward at a stop and rolling back after Park was not engaged on the column shifter. Other reports cover P052E crankcase ventilation codes, piston damage with smoke and power loss, a cylinder head cover oil leak, and a failed AMG rear differential.

Most of these reports concern a recall, not actual failures. A recall for a steering rack locknut that could crack left many owners waiting, because dealers had no parts and no date for the remedy. Actual failures are fewer but serious. Electric power steering can quit with a malfunction warning, and two crash reports describe drivers losing steering on a curve or hitting a wall. Dealers sometimes find no fault. Other complaints mention rack and pinion noise around 57,000 miles and a steering wheel surface that deteriorates.

Roof bonding failures are the main pattern. The exterior panel between the windshield and the panoramic roof can come loose at highway speed and strike the car or traffic behind it. Some owners say their VIN was left out of the related recall. Sunroofs that will not close, convertible tops that leak or will not operate, and headliner fabric pulling away also come up. Other reports describe front doors that swing shut hard enough to bruise legs and water under the floor that set off ABS faults.

The most serious reports describe airbags that did not deploy in frontal crashes, and several occupants were hurt. Others describe a steering-wheel airbag firing while backing out of a driveway and a knee airbag injuring a short driver. The most common fault outside of crashes is an airbag warning light, often traced to a bad clock spring or control unit between about 46,000 and 72,000 miles. A dead horn or a rattling steering column sometimes comes with it. Owners covered by a Takata recall also report waiting for parts.

Loud squealing, squeaking, or grinding is the most common brake complaint. It often starts soon after purchase and comes back after the pads are replaced. Some owners needed new brakes by 9000 to 14,000 miles. Because only one rear wheel has a pad wear sensor, one owner's other rear pad wore down to metal with no dash warning. More serious reports describe sudden emergency braking with nothing in the road, a pedal that did nothing for several seconds, and a crash after the car failed to slow.

Unintended acceleration while pulling into or stopping in a parking space is the main risk, and two crash reports describe cars hitting walls. Dealers often cannot reproduce it. Owners also describe adaptive cruise control making a full-force emergency stop on an empty road, lane keeping that bounces between the lane lines, and a cruise set speed that cannot be cleared. The transmission can also drop into neutral and slam back into gear after about 20 seconds. Some owners blame the factory performance tires for sliding in light snow.

Most of these complaints are about glass and adhesive bonds that fail. Rear windows come loose when their bonding fails, at around 50,000 to 70,000 miles, and owners say their VIN was not covered by the related recall. The exterior panel between the windshield and sunroof can also come off at highway speed. A sunroof that shattered at speed sprayed glass on the people inside and caused minor injuries. Other reports mention wind getting in through the sunroof and a side mirror that makes cars look farther away than they are.