What is the main role of a vehicle's brake system?

The main role of a vehicle's brake system is to decrease speed or stop the vehicle. The brake system is a critical safety feature in any automobile, designed to slow down or stop the vehicle's motion effectively when the driver applies the brakes. This function allows for safe maneuvering, responding to traffic situations, and avoiding potential accidents.

When brakes are engaged, they create friction against the wheels, thereby reducing their speed or bringing them to a complete stop. This is essential for maintaining control over the vehicle, especially in emergency situations where immediate stopping is required.

The other options do not accurately describe the primary function of the braking system. While improving fuel efficiency might be a consideration in vehicle design, it is not the function of the brake system itself. Similarly, controlling engine temperature is linked to the vehicle's cooling system, and enhancing steering precision relates to the steering mechanisms, not the brakes. Thus, the correct understanding of a vehicle's brake system revolves solely around its ability to decrease speed or stop the vehicle when necessary.