When testing the trailer service brakes, what is one of the first actions to take?

Checking the normal air pressure in the system is a vital first step when testing the trailer service brakes. Proper air pressure ensures that the brakes can function effectively and respond to the driver's input. The air brake system relies on adequate pressure to apply the brakes correctly; insufficient pressure may indicate potential issues such as leaks or needs for system adjustments, compromising braking performance and safety.

When the correct air pressure is established, it sets the foundation for further brake tests, such as engaging the parking brake or inspecting specific components of the dolly. These later steps rely on having confirmed that the air supply is within the appropriate range for effective brake operation. Thus, starting with a check of the normal air pressure is critical to maintaining operational safety and efficacy for the entire braking system.