2021 BMW 4-Series Reliability Score & Common Problems

Owners of the 2021 BMW 4-Series report several power train issues, with multiple complaints highlighting problems related to the starter motor and auxiliary battery, which affect the vehicle's ability to start. Some owners describe drivetrain service warnings prior to failure, typically around early morning starts. Another pattern involves rodent damage to soy-based engine wiring, leading to compromised vehicle functions and drive train malfunctions. Additionally, a few owners report transmission issues, including stalling and lack of response from the accelerator, with one incident resulting in a torn rotator cuff due to a violent jolt. These issues appear at various mileage points, with one report noting a rear differential failure at approximately 33,000 miles. Safety implications include potential for injury and vehicle inoperability, which may be critical for prospective buyers to consider.

Owners report issues with the engine starter and motor mounts on the 2021 BMW 4-Series. Complaints frequently mention engine starter relay malfunctions linked to a recall for potential corrosion, leading to overheating and fire risks, with recommendations to park the vehicle outside. Multiple owners describe motor mount failures, with symptoms such as vehicle hesitation and abnormal pulling sounds, typically occurring around 52,000 to 60,000 miles. These issues pose safety implications, particularly concerning the fire risk associated with the engine starter relay. Prospective buyers should be aware of these concerns and verify recall repairs and motor mount condition before purchasing.

Owners of the 2021 BMW 4-Series report issues with the airbag system, with multiple complaints indicating a "restraint system warning" that suggests reduced functionality of airbags and seatbelt tensioners. One complaint involves a crash where the airbags deployed after a sudden unintended acceleration incident, resulting in an injury. Another owner mentions a persistent "passenger restraint failure" code appearing within three months of ownership, requiring costly repairs and raising concerns about airbag deployment in an accident. Additionally, some owners report issues with the quality of the airbag leather cover, leading to recommendations for replacement. These complaints typically emerge around 18,000 miles, highlighting potential safety implications if unresolved.

Owners of the 2021 BMW 4-Series report issues primarily related to the throttle body actuator and the EVAP system. A common failure involves the throttle body actuator, where failure results in the engine dropping to idle speed, significantly reducing vehicle speed and posing a safety risk if it occurs at high speeds. Another reported issue is the failure of the EVAP system, often indicated by an illuminated check engine light. Additionally, some owners experience gas fumes entering the cabin, leading to health symptoms such as nausea and respiratory issues. These issues can occur at varying mileages, and the throttle body actuator problem is noted to potentially cause dangerous situations if the vehicle loses power unexpectedly.

Owners of the 2021 BMW 4-Series report issues with the seat belt system, primarily involving the seatbelt assembly's mechanical components. Complaints frequently mention a flimsy seatbelt arm that breaks easily, creating a potential safety hazard with a jagged edge at eye level. Another common issue involves the seat belt retractor, which repeatedly fails shortly after repair attempts, leading to non-functional seat belts. Additionally, some owners describe seat belts failing to detach due to obstructions, such as candy lodged in the buckle, requiring forceful removal. These problems are reported at relatively low mileage, around 10,000 miles, and raise concerns about the vehicle's safety features not performing as expected.

Owners of the 2021 BMW 4-Series report issues related to suspension components, particularly concerning engine mounts and front axle support. Complaints frequently mention engine mounts failing around 43,000 miles, which some owners find unexpected given typical expectations for these parts. Additionally, multiple owners describe problems with the front axle support and right front control arm bearing bracket, leading to persistent alignment issues and accelerated tire wear, despite limited mileage. These issues are noted to cause safety concerns, as one owner was advised that driving with failed engine mounts is dangerous, and alignment problems could affect vehicle handling. Used car buyers should be aware of these patterns, especially if purchasing a vehicle with mileage in the 40,000 range or experiencing similar symptoms.

Owners of the 2021 BMW 4-Series report issues related to steering and vehicle electronics. One complaint describes a failure of the Electric Motor Electronics and 12v Battery, resulting in a loss of control over vehicle electronics, including steering and braking, with implications for vehicle safety. This issue was preceded by problems starting in late April, with servicing in early May. Another owner reports an intermittent vibration at highway speeds attributed to a right front wheel being out of round, despite no known impact damage. The dealer's initial repair did not resolve the issue, and the owner suspects that the combination of run-flat tires and low-profile wheels may contribute to the problem. These reports suggest potential safety risks and persistent issues that may be relevant for prospective buyers to consider.