What is the primary function of a seat belt pretensioner?

The primary function of a seat belt pretensioner is to automatically tighten the seat belt during a collision. This mechanism is crucial for enhancing passenger safety; by reducing slack in the belt, it ensures that the occupant is held securely in place at the moment of impact. This rapid tightening helps to minimize the risk of injury by preventing the occupant from moving forward excessively, which could lead to serious harm from the steering wheel, dashboard, or windshield.

The additional options serve different purposes. Decreasing fuel consumption is unrelated to the functionality of seat belts. Providing a warning for the driver to buckle up is generally a feature of seat belt reminders but does not involve the pretensioner's role in an accident. Adjusting seat position for comfort is a feature of seat mechanisms, not related to the safety function of seat belts. Thus, while all these features play important roles in vehicle safety and comfort, the pretensioner's specific task is to secure the occupant effectively during a collision.