Checking vacuum supply to the power booster

The power brake booster must have the right amount of vacuum to work properly. With insufficient vacuum, the driver must step up the pressure force on the foot pedal to activate the brake. Excessive vacuum is not a problem because the servo device is dimensioned to work with the maximum vacuum that the motor can create. Gasoline engines create a vacuum in the intake manifold in idle mode. Diesel engines use a special engine-driven vacuum pump or a built-in intake manifold throttle valve that is activated when the power booster needs a vacuum.

The minimum required vacuum for proper operation of the power brake booster is 0.54 bar.

Engines having a system for camshaft adjustment in some cases have a lower vacuum and be harder to press the brake pedal. Vehicle manufacturers solve this problem by installing a power sensor vacuum sensor so that the electronic system regulates the operation of the camshaft control system when it is necessary to create the required vacuum or install an additional vacuum pump. Also, operating the engine at higher altitudes results in a lower vacuum. At every 300 m above sea level, the vacuum is reduced by 33 mbar.

Vacuum measurement on the vacuum hose of a power booster.

The test is performed by disconnecting the vacuum hose from the power booster when the engine is switched off. A manometer for measuring the vacuum is installed on the free end of the hose. Start the engine and in idle mode complains vacuum value. The vacuum should have a value below 0.54 bar. If the pressure is higher, the cause of the weaker vacuum is found.

To checking the vacuum supply to the power booster, follow these steps:

Preparation for measurement

When the engine is off, disconnect the vacuum hose from the servo. Connect a vacuum gauge to the end of the vacuum hose.

Vacuum measurement

Start the engine. Read the magnitude of the vacuum when the engine is idling. Compare the obtained result with the required values from the information system for a given vehicle (when not specified, the expected upper value of vacuum is 0.54 bar).

Analysis and completion of measurements

If the vacuum value is insufficient, check for vacuum leaks, supply hose restrictions, or engine malfunction. After measuring, remove the manometer and connect the vacuum hose to the servo device.