The passenger compartment remained stable in the frontal offset test.  Dummy readings showed good protection of the knees and femurs of both driver and passenger.  Mercedes-Benz showed that a similar level of protection would be provided for occupants of different sizes and to those sat in different positions.  Protection of the passenger was good for all critical body areas.  In the full-width rigid barrier test, protection of the driver and rear passenger was good or adequate.  In the side barrier test, protection of the dummy was good for all critical body areas and maximum points were scored.  However, in the more severe side pole test, dummy readings of rib compression indicated weak protection of the chest.  Tests on the front seats and head restraints demonstrated good protection against whiplash injury in the event of a rear-end collision.  A geometric assessment indicated weak whiplash protection for occupants of the rear seats.  The C-Class Cabriolet has, as standard, an autonomous emergency braking system.  Tests showed good performance of the functionality of this system at the low speeds at which many whiplash injuries are caused, with collisions avoided or mitigated.

In the frontal offset test, protection of both the 6 year and 10 year dummy was good or adequate.  However, in the side barrier test, the head of the 10 year dummy contacted the metal frame of the folding roof and protection was rated as poor, based on the resulting high decelerations.  The C-Class Cabriolet automatically disables the front passenger airbag when a rearward-facing child restraint is positioned there.  Mercedes-Benz showed that the system worked robustly and it was rewarded. Care is needed when installing the Group I ISOFIX restraint in the rear seats as the top tether anchorage is obscured.  Otherwise all of the seats for which the car is designed could be installed and accommodated without problem.

The C-Class Cabriolet has an 'active' bonnet.  Sensors detect when a pedestrian has been struck and actuators raise the bonnet to provide greater clearance to the stiff structures in the engine compartment.  Mercedes-Benz showed that the system worked robustly for different pedestrian statures and over a wide range of speeds, so tests were conducted with the bonnet in the raised position.  Results were good at almost all test locations.  The bumper provided good protection to pedestrians' legs and maximum points were scored in these tests.  However, protection of the pelvis was predominantly poor.  A pedestrian-detecting autonomous braking system is available.  However, as this is an option it was not tested as part of this assessment.

A driver-set speed limiter and a seatbelt reminder for the front and rear seats are fitted as standard.  Also standard is the autonomous emergency braking system.  Tests of this system at highway speeds demonstrated adequate performance.  A lane assistance system is available as an option but is not included in this assessment.