If the rear bench seat/rear seat and seat backrest are not engaged, they could fold forwards, e.g. during sudden braking or in the event of an accident.
If this were the case, the vehicle occupant would be forced into the seat belt by the rear bench seat/rear seat or by the seat backrest. The seat belt would not be able to provide the intended protection and could cause additional injury.
Objects or loads in the boot cannot be restrained by the seat backrest.
The seat belt could become trapped and thus damaged when folding back the seat backrest.
back until it engages. Left and right seat backrests: if the seat backrest is not engaged and locked, this will be shown on the multifunction display on the instrument cluster.
A warning tone will also sound.
Centre seat backrest: if the seat backrest is not engaged and locked, red lock verification indicator 
will be visible.