The BMW 4 series convertible is structurally similar to the BMW 3 series tested in 2019 and shares the same level of safety equipment.  Additional tests have been done where the performance of the cars might differ but, otherwise, test results are taken from the 3 series.

The passenger compartment remained stable in the frontal offset test.  Dummy readings indicated good protection of the knees and femurs of both the driver and passenger.  BMW showed that a similar level of protection would be provided to occupants of different sizes and to those sitting in different positions.  In the full-width rigid barrier test, protection of the driver and rear passenger was good or adequate for all critical body areas.  The car scored maximum points in the side barrier test, with good protection of all critical body areas.  In the more severe pole impact, protection of the chest was adequate and that of other critical body areas was good.  Tests on the front seats and head restraints demonstrated good protection against whiplash injuries in the event of a rear-end collision.  A geometric assessment of the rear seats also indicated good whiplash protection.  The standard-fit autonomous emergency braking (AEB) system scored maximum points in tests of its functionality at low, city-driving speeds, with collisions avoided in all test scenarios.

In the frontal offset and side barrier crash tests, protection of both the 6- and 10-year dummies was good or adequate for all critical parts of the body.  The front passenger airbag can be disabled to allow a rearward-facing child restraint to be used in that seating position.  Clear information is provided to the driver regarding the status of the airbag, and the system was rewarded.  Some child restraint systems could not be properly installed in the car owing to the shape of the rear seats but most could be properly fitted and accommodated.

The 4-series convertible has an 'active' bonnet.  Sensors in the bumper detect when a pedestrian has been struck and actuators lift the bonnet to provide greater clearance to the stiff structures in the engine compartment.  BMW showed that the system performed robustly for a variety of pedestrian statures and over a wide range of speeds.  Accordingly, the bonnet was tested in its deployed, raised position and protection over its surface was almost entirely good, poor results being recorded only along the base of the windscreen and on the stiff windscreen pillars.  The bumper provided good protection to pedestrians' legs at all test points.  Protection of the pelvis was mixed also good in all of Euro NCAP’s tests.  The AEB system can detect pedestrians and cyclists as well as other cars.  In tests of its response to such vulnerable road users, the system performed well, with collisions avoided or mitigated in all test scenarios.

The 4-series convertible has a seatbelt reminder as standard equipment for the front and rear seats.  Lane support helps prevent inadvertent drifting out of lane by warning the driver and gently correcting the vehicle's path.  The standard-fit speed assistance system uses a camera to determine the prevailing speed limit and presents this information to the driver, allowing the limiter to be set appropriately.  The AEB system performed well in tests of its response to other cars at highway speeds, with collisions avoided or mitigated in all test scenarios.