What is the main purpose of the leak-down test?

Answer: B — To assess air pressure in the system

The primary purpose of the leak-down test is to assess air pressure in the braking system. This test is essential for ensuring that the air brake system maintains the required pressure for optimal performance. It helps identify any potential leaks in the air system that could impact the brakes' ability to function effectively. By measuring how quickly pressure drops, a technician can determine if there’s an air leak that needs to be addressed. A successful leak-down test indicates that the system can hold air pressure adequately, which is crucial for safety and reliability when operating a vehicle with air brakes. This focus on air pressure differentiates the leak-down test from other checks, such as assessing brake fluid levels or evaluating brake effectiveness, which are governed by different diagnostic criteria.