Which of the following systems is dependent on effective air pressure to operate?

The service brake system is dependent on effective air pressure to operate because it relies on compressed air to create the force necessary for braking. In vehicles equipped with air brakes, air pressure is utilized to engage the brake components, allowing them to apply pressure to the brake drums or discs and slow down or stop the vehicle. This system is designed to be very reliable, as it uses the principle of air pressure to provide consistent and powerful braking performance.

The other systems listed do not operate primarily through air pressure. The electrical braking system relies on electrical signals and motors to function. The steering system utilizes mechanical or hydraulic force to steer the vehicle and does not depend on air pressure for its operation. The suspension system is focused on supporting the vehicle's chassis and providing a smooth ride, typically involving springs and shock absorbers, which are also independent of air pressure in their standard configurations.