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Component Test-Brake Booster-Vacuum Boost

WARNING: This page is about a different car, the 2019 Ford F-550 Super Duty, 2019 Ford F-450 Super Duty, 2019 Ford F-350 Super Duty, and 2019 Ford F-250 Super Duty. However, it is still accessible from the selected car via links, so may be relevant.
  1. NOTE: If oil contamination is found and the vacuum system is not replaced during brake booster replacement, booster failure will occur again.

    If equipped with a diesel engine, inspect the brake booster, vacuum lines and check valve for signs of oil.

    • If oil is found in the vacuum line(s) or check valve, replace the brake booster, all vacuum lines, vacuum reservoir and the vacuum pump at the same time.

  2. Disconnect the check valve from the brake booster and connect a suitable vacuum/pressure tester to the check valve.
  3. Apply the parking brake, start the engine and place the transmission in NEUTRAL.

    • Allow the engine to reach normal operating temperature.

  4. NOTE: Subtract approximately 3.38 kPa (1 in-Hg) from the specified reading for every 304.8 m (1, 000 ft) of elevation above sea level.

    Verify that vacuum is available at the vacuum sensor/check valve with engine running at normal idle speed.

    • The vacuum gauge should read between 51-74 kPa (15-22 in-Hg) on vehicles not equipped with a vacuum pump and 70-85 kPa (20-25 in-Hg) on vacuum pump-equipped vehicles.

    • If specified vacuum is available, stop the engine, connect the check valve and continue with Step 6.

    • If specified vacuum is not available, continue with Step 5.

  5. Disconnect the vacuum sensor/check valve from the vacuum hose and verify that the specified vacuum is available at the hose with the engine at idle speed and the transmission in NEUTRAL.

    • If specified vacuum is available, stop the engine, install a new check valve and check the system for normal operation.

    • If specified vacuum is not available on gasoline engine vehicles, stop the engine, connect the vacuum hose to the check valve and diagnose the no/low vacuum condition. REFER to: Engine .

    • If specified vacuum is not available on diesel engine vehicles, inspect the vacuum hose and install new as necessary. If vacuum hose is ok, install a new vacuum pump. REFER to: Brake Vacuum Pump .

  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.

    • 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), install a new brake booster vacuum sensor/check valve and retest.

    • If condition still exists, install a new brake booster. REFER to: Brake Booster .

    • If the brake pedal feels the same as noted with the engine operating, the check valve is functioning properly.

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