2021 BMW 4 Series Reliability Report

The recurring symptom is a car that will not move from a stop. Drivers press the accelerator at a green light and get no response or a stall. In one case the car then jolted hard forward, and an injury followed. A dealer traced one no-go event, with the power train warning lit, to a rear differential that had leaked its oil and seized. Other reports cover a failed starter motor with a weak auxiliary battery, and rodent-chewed engine wiring that limited engine power.

Failed motor mounts are the clearest mechanical pattern. They are reported between 52k and 60,000 miles, with hesitation at startup and an abnormal pulling sound. Owners say the mounts should not wear out this early, including on a car bought certified pre-owned. The other reports concern the starter recall. Dealers and the manufacturer say no remedy is available and give no timeline. One buyer says the selling dealer did not explain the open recall before the sale.

The main complaint is restraint system warnings that will not clear. On cars never in a crash, drivers see messages saying airbag and seatbelt tensioner function is reduced. One owner was quoted $2700 to fix a passenger restraint fault and had to pay it personally. A crash report describes brakes that failed while parking, then sudden acceleration into another vehicle. The airbags deployed and the car was totaled. Separately, a steering wheel airbag cover folding in at the edge appears at about 18,000 miles.

Loss of power at speed is the most serious complaint here. A failed throttle body actuator puts the engine in a safe mode near idle, around 500 rpm. The car can then crawl at only a few mph, even in freeway traffic. Other reports describe an EVAP system failure with the check engine light on. One owner reports strong gasoline fumes inside the cabin and links them to repeated illness.

These complaints are about seat belt hardware that breaks or jams. The plastic arm that extends to hand the belt to front occupants can snap and leave a rigid, jagged piece at eye level. Dealers have called that misuse. Belt retractors break again within days of being repaired, and dealers decline further coverage. Buckles that would not release, reported at about 10,000 miles, were blamed on candy lodged inside.

Failed engine mounts show up here at 43,000 miles. They were found during a brake service, called unsafe to drive, and quoted at $3000 just after the warranty ran out. The other report describes a car that keeps falling out of alignment. The owner suspects the front axle support and control arm bracket are separating. Repeated paid alignments have not fixed it, and the tires wear quickly.

The main symptom is vibration at highway speeds. A dealer traced it to an out-of-round front wheel, but the shaking continued after the repair. The owner suspects the run-flat tires and low-profile wheels. The other report describes a sudden failure of the electric motor electronics and the 12v battery. That owner says the failure can cut power to steering, braking, and propulsion together.