Vacuum, Checking

WARNING: This page is about a different car, the 2023 Audi SQ8, 2023 Audi RS Q8, and 2023 Audi Q8. 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 (14.69 psi) and it decreases dramatically at higher altitudes (approximately 100 mbar (1.45 psi) every 1000 meters higher) 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.

Procedure

-- Connect the Brake Servo Tester:VAS6721 . Refer to BRAKE BOOSTER TESTER, CONNECTING .

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

Fig 1: Identifying VAS 6721 Shut-Off Valves

Courtesy of AUDI OF AMERICA, LLC

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

-- Start the warm (above 60 °C (140 °F)) engine and press the accelerator pedal one time quickly (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:VAS6213 for comparison. Refer to VACUUM, CREATING WITH HAND VACUUM PUMP .

TIP:

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