If the rear seat backrests are not locked, they could fold forwards in the event of an accident, heavy braking or sudden changes of direction.
As a result, child restraint systems cannot perform their intended protective function. Rear seat backrests that are not locked can also cause additional injuries, e.g. in the event of an accident.
If the left and right seat backrests are not engaged and locked in place, this will be shown on the multifunction display of the instrument cluster.
If the centre seat backrest is not engaged and locked in place, the red lock verification indicator will be visible.
If the child restraint system is equipped with a Top Tether belt:
The risk of injury can be reduced by a Top Tether. The Top Tether belt facilitates an additional connection between the child restraint system attached with ISOFIX or i‑Size and the vehicle.
upwards More. 
of the Top Tether anchorage 
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under the head restraint between the two head restraint bars. 
of the Top Tether belt into the Top Tether anchorage without twisting. . Comply with the child restraint system manufacturer's installation instructions when doing so. of the Top Tether anchorage . downwards More. Make sure that you do not interfere with the correct routing of the Top Tether belt .