Automotive Service Excellence (ASE) Brakes Certification Practice Exam

When a vehicle's brakes emit a hissing sound, it is typically indicative of an issue with the brake booster or a vacuum leak associated with it. The brake booster assists in amplifying the force applied to the brake pedal, which is crucial for effective braking performance. A hissing noise often suggests that there is an air leak in the brake booster system, which can compromise the boost it provides and lead to reduced braking efficiency.

In diagnosing this issue, it is important to inspect the brake booster for damage, check the vacuum source, and examine the vacuum lines for any cracks or disconnections. This thorough inspection helps to identify and rectify the underlying problem, ensuring that the braking system operates optimally and safely.

While the other options—checking the brake fluid level, inspecting the condition of the brake pads, and measuring the size of the brake rotors—are all important maintenance tasks, they are not directly related to the hissing sound. The hissing specifically indicates a potential issue with the brake booster or vacuum lines, making that the priority for diagnosis and repair in this scenario.