Which vacuum component provides brake assist using engine vacuum?

• A. Vacuum reservoir.
• B. MAP sensor.
• C. PCV system.
• D. Brake booster.

Answer: (D)

Brake boost using engine vacuum is achieved by the brake booster. This device sits between the brake pedal and the master cylinder and uses the vacuum from the engine to create a pressure differential across a diaphragm. When you press the pedal, the booster uses that vacuum to add force to the master cylinder piston, so you get more braking with less pedal effort. A vacuum reservoir can store extra vacuum for brief periods, but it’s the brake booster that actually provides the assist.

The other components don’t provide this assist. The MAP sensor monitors manifold pressure for engine management, not braking. ThePCV system uses vacuum to vent crankcase gases back into the intake, not to aid braking.