Vacuum, Checking

WARNING: This page is about a different car, the 2025 Volkswagen Jetta. However, it is still accessible from the selected car via links, so may be relevant.

The average earth atmospheric air pressure at sea level (N. N.) is 1013 mbar.

At higher altitudes the air pressure decreases dramatically (approximately 100 mbar (1.45 psi)/1000 m altitude).

Local and time fluctuations also influence the vacuum.

A cold engine, the A/C switched on as well as the engine simply idling can negatively influence the vacuum.

-- Check all the vacuum hoses beforehand for damage (for example, tears or damage caused by animals) and secure fit.

-- Connect the Brake Servo Tester :VAS 6721 . Refer to Brake Servo Tester .

-- Open the shut-off valve -A-.

-- Close the shut-off valves -B and C-.

Fig 1: Identifying VAS 6721 Shut-Off Valves

Courtesy of VOLKSWAGEN GROUP OF AMERICA, INC.

-- Start the warm (above 60 °C (140 °F)) engine and press the accelerator pedal once briefly (engine speed higher than 2, 000 RPM).

-- Read the displayed measured value.

Normally (see note), the vacuum should be between 600 and 950 mbar (8.7 and 13.78 psi) (depending on the engine installed).

Check the vacuum system for leaks if the measured value is not reached, even though all requirements (see notes) are met.

-- Create a vacuum using the Hand Vacuum Pump :VAS 6213 for comparison. Refer to VACUUM, CREATING WITH Hand Vacuum Pump .

Opening the shut-off valve -B- makes it easier to remove the hose connections and the adapter.