The passenger compartment of the C4 remained stable in the frontal offset test. Dummy readings demonstrated good protection of the knees and femurs of both the driver and passenger dummies. Citroën showed that the same level of protection would be provided to the upper legs of occupants of different statures to the test dummy and to those sitting in different positions. However, dummy readings also indicated marginal protection of the front passenger's lower leg. Analysis of decelerations of the impact trolley and of the deformed impact barrier after the test indicated that the C4 would be a reasonably benign collision partner. In the full-width rigid barrier test, good or adequate protection was provided to all critical parts of the body. The C4 scored maximum points in both the side barrier and side pole impacts, with good protection of all critical body regions. The extent to which sideways excursion (movement of the occupant to the opposite side of the car) was mitigated was rated as [poor] [weak], and no counter-measure is fitted to prevent occupant to occupant injuries in side impacts. Tests on the front seats and head restraints demonstrated good protection against whiplash injuries in the event of a rear-end collision. A geometric analysis of the rear seats also indicated good whiplash protection. The C4 is equipped with 'In-Crash Braking', a system designed to prevent secondary impacts after a collision. However, the system did not meet Euro NCAP's requirements and was not rewarded.

In the frontal offset test, protection of the neck of the 10 year dummy was rated as marginal, based on readings of tensile forces. Otherwise, protection of the 10 and 6 year dummies was good or adequate. In the side barrier impact, protection of all critical body areas was good for both child dummies. 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. All of the child restraint types for which the C4 is designed could be properly installed and accommodated.

The protection provided by the bonnet to the head of a struck pedestrian was predominantly good or adequate over the bonnet surface but tests on areas around the base of the windscreen and on the stiff windscreen pillars indicated poor protection. The bumper provided good protection to pedestrians’ legs and the pelvis area was also well protected, the C4 scoring maximum points in both of these areas. The autonomous emergency braking (AEB) system of the C4 detects some vulnerable road users as well as other vehicles. In tests of its response to pedestrians, the AEB system showed marginal performance, with avoidance or mitigation only in some of the test scenarios.