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Component Test- Brake Booster

WARNING: This page is about a different car, the 2020 Ford F-150. However, it is still accessible from the selected car via links, so may be relevant.
  1. Disconnect the vacuum tube from the brake booster and connect a suitable vacuum/pressure tester to the vacuum tube.
  2. Apply the parking brake, start the engine and place the transmission in NEUTRAL.

    • Allow the engine to reach normal operating temperature.

  3. Verify that vacuum is available at the vacuum tube with engine running at normal idle speed.

    • The vacuum gauge should read above 41 kPa (12 in-Hg).

    • If specified vacuum is available, stop the engine, connect the tube and proceed to Step 6.

    • For vehicles not equipped with a vacuum pump, if specified vacuum is not available, stop the engine, connect the tube and continue with Step 4.

    • For vehicles equipped with a brake vacuum pump, if specified vacuum is not available proceed to Step 5.

  4. Disconnect the vacuum tube from the engine, connect the vacuum gauge to the vacuum port on the engine and verify the specified vacuum is available with the engine at idle speed and the transmission in NEUTRAL.

    • The vacuum gauge should read above 41 kPa (12 in-Hg).

    • If the specified vacuum is available, install a new vacuum tube assembly and check the system for normal operation.

    • If specified vacuum is not available, stop the engine, diagnose the engine vacuum condition. REFER to: Engine .

  5. Disconnect the vacuum tube from the vacuum pump and check for the specified vacuum at the vacuum pump with the engine at idle speed and the transmission in NEUTRAL.

    • The vacuum gauge should read above 41 kPa (12 in-Hg).

    • If the specified vacuum is available at the pump, install a new vacuum tube assembly and check the system for normal operation.

  6. Apply the brake pedal several times to exhaust all vacuum from the system.
  7. Apply the brake pedal and hold it in the applied position. Start the engine and verify that the brake pedal moves downward after the engine starts.

    • If the brake pedal moves, the brake booster is operating correctly. Proceed to Step 8.

    • If the brake pedal does not move, install a new brake booster. REFER to: Brake Booster .

  8. Operate the engine a minimum of 20 seconds at idle. Stop the engine and let the vehicle stand for 10 minutes, then apply the brake pedal. The brake pedal feel should be the same as that noted with the engine operating.

    • If the brake pedal feels hard (no power assist), proceed to Step 9.

    • If the brake pedal feels the same as noted with the engine operating, the vacuum system does not have a gross leak.

  9. Disconnect vacuum harness from booster. Using an external vacuum pump apply vacuum 50 kPa (15 in-Hg) to the brake booster and leave the vacuum applied to the brake booster for 10 minutes.

    • Check the vacuum gauge for vacuum loss. If loss in vacuum is equal to or more than 1.5 kPa (.44 in-Hg) proceed to Step 10.

    • If the vacuum loss is less than 1.5 kPa (.44 in-Hg) replace the vacuum harness.

  10. Remove the brake master cylinder. REFER to: Brake Master Cylinder . Inspect the O-ring seal between brake master cylinder and brake booster for a damage.

    • If a damaged O-ring seal is found, install a new O-ring seal, install the brake master cylinder and repeat step 9 to verify the issue is resolved.

    • If difference in vacuum sensor reading of more than 1.5 kPa (.44 in-Hg) is still observed install a new brake booster. REFER to: Brake Booster . Check the system for normal operation. If the problem still exists install a new vacuum harness.

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