What is the first step after coupling air hoses to restore air pressure?

The first step after coupling air hoses to restore air pressure is to make a 20 psi brake pipe reduction. This action is crucial because it initiates the flow of air through the newly connected hoses and begins the pressurization process in the brake pipe. By creating a reduction, the system detects that air is flowing and allows for proper communication between the cars.

When a 20 psi reduction is made, it ensures that all components of the air brake system are functioning correctly, and it establishes a baseline pressure throughout the train. This is important for maintaining safety and control, as it prepares the air brake system for subsequent actions, such as releasing the brakes.

The other options involve actions that may occur at different stages in the air brake system operations, but they are not the primary initial step required for restoring air pressure immediately after coupling the hoses.