A handful of limousines are being called back for a potentially faulty occupant recognition system that may not tighten the seatbelts in the event of a collision.

Mercedes-Benz Australia has issued a recall for nine 2018 model-year S-Class sedans over concerns the Pre-Safe safety system may not engage even if a passenger is in the seat.

According to the German marque, affected vehicles may not detect when a seatbelt is engaged, which will see a warning tone sound and a symbol illuminate in the instrument cluster.

Should the condition occur, the vehicle's 'Pre-Safe' function may not engage – which pre-tensions the seatbelts if the vehicle detects an accident is about to occur. This affects all seatbelts.

Mercedes-Benz says the "complete effect of the restraint system could not be ensured" if this happens.

There are nine units affected by this recall, sold between 19 September 2018 and 31 October 2018 – a VIN list is available here.

Owners of the recalled S-Class models will be contacted by Mercedes-Benz directly to arrange the repair of their vehicle, free of charge.