ASE Brakes Certification Practice Exam 2025 – Complete Study Resource

When testing the internal function of a vacuum power booster, the desired outcome after turning off the engine indicates that the booster is working properly. If the brake pedal holds steady, it signifies that the internal seals within the power booster are intact and maintaining vacuum pressure.

A correctly functioning vacuum power booster relies on a vacuum source created by the engine to assist in applying force to the brake system. When the engine is turned off, the vacuum in the booster should remain stable for a sufficient period, allowing the brake pedal to maintain its position. This stability reflects effective sealing and functionality, demonstrating that the brake booster is not leaking internally.

In contrast, if the pedal were to pulsate rapidly, sink slowly, or rise slowly, it would suggest potential issues. A pulsating pedal indicates erratic pressure, while sinking slowly points to possible fluid leakage or internal failure. A slowly rising pedal might suggest that the booster is not holding vacuum correctly or that there is a pressure build-up in the system. Therefore, a steady brake pedal after engine shutdown confirms a properly functioning vacuum power booster.