How is the vacuum booster tested in a brake system inspection?

The vacuum booster in a brake system is tested primarily by checking the pedal pressure after starting the engine. This is because the vacuum booster assists in reducing the amount of effort needed on the brake pedal by amplifying the force applied by the driver.

When the engine is started, the vacuum should engage the booster, allowing the brake pedal to feel noticeably lighter when pressed. A successful test would show that the pedal moves downward easily with less pressure compared to when the engine is off. This indicates that the vacuum system is functioning properly and providing the necessary assistance to the braking system.

Other methods, such as observing for brake fluid leaks or measuring pedal travel while driving, do not directly assess the vacuum assist's effectiveness. Similarly, inspecting the brake fluid level is important for overall brake system maintenance, but it does not evaluate the operation of the vacuum booster itself. Thus, checking the pedal pressure after starting the engine is the most effective means to verify the functionality of the vacuum booster.