What is the purpose of performing a vacuum test on the brake system?

• A. Verify adequate engine vacuum for the brake booster and detect leaks in the vacuum supply line.
• B. Measure brake fluid pressure to assess braking efficiency.
• C. Test the brake lines for corrosion.
• D. Check tire pressure to ensure consistent braking.

Answer: (A)

The brake booster relies on engine vacuum to multiply the force you apply to the brake pedal. A vacuum test checks that there is enough vacuum at the booster and that the vacuum supply line is not leaking. If vacuum is insufficient or a leak is present, the booster can’t provide assist, making the pedal feel hard and braking less effective. This test specifically targets the vacuum side of the system, not the hydraulic brake fluid, brake lines for corrosion, or tire pressures. Common causes of vacuum issues include a cracked or loose vacuum hose, a bad check valve, or a leak in the intake/vacuum source.