Leak Test

-- Connect the Brake Servo Tester:VAS 6721 . Refer to BRAKE BOOSTER TESTER, CONNECTING .

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

Fig 1: Identifying VAS 6721 Shut-Off Valves

Courtesy of AUDI

-- 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).

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

-- Open the shut-off valve -C- to evacuate the brake booster.

Fig 2: Identifying VAS 6721 Shut-Off Valves

Courtesy of AUDI

-- Turn off the engine.

-- Read the displayed measured value and write it down.

The vacuum may drop 400 mbar (5.8 psi) in 12 hours.

TIP:

The vacuum will drop considerably within a few seconds if there are large leaks.

-- If the pressure drop is large, look for the area with the leak:

A - Testing the vacuum near the brake booster

Fig 3: Identifying VAS 6721 Shut-Off Valves

Courtesy of AUDI

-- Close the shut-off valve -A- after creating the vacuum to check the brake booster vacuum system.

B - Testing the vacuum near the check valve, vacuum hoses with connectors and vacuum pump/intake manifold

Fig 4: Identifying VAS 6721 Shut-Off Valves

Courtesy of AUDI

-- Close the shut-off valve -C- after creating the vacuum to check the vacuum system from the Brake Servo Tester:VAS 6721 up to the intake manifold or up to the vacuum pump.

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