Operation Check When Not Using Measuring Devices

WARNING: This page is about a different car, the 2021 Subaru Ascent. However, it is still accessible from the selected car via links, so may be relevant.

CAUTION: When checking operation, be sure to apply the parking brake securely.

When an operation check is performed with no measuring devices, a faulty part cannot be identified correctly. But it is possible to identify the outline of the defect by performing the check according to the following procedures.

AIR TIGHTNESS CHECK

NOTE:

In case of defective operation, inspect the condition of the check valve and vacuum hose as well.
Replace them if faulty, and perform the test again.
If no improvement is observed, check precisely with gauges.

Start the engine, and idle it for 1 to 2 minutes, then turn it OFF.
Depress the brake pedal several times applying the normal pedal force.
NOTE: The pedal stroke should be the longest at the 1st depression, and it should become shorter at each successive depression.
If no change occurs in the pedal height when pressed, the vacuum booster assembly is faulty.

Courtesy of SUBARU OF AMERICA, INC.

CHECK OPERATION

While the engine is OFF, depress the brake pedal several times applying the same pedal force, to check for a change in pedal height.

Courtesy of SUBARU OF AMERICA, INC.
With the brake pedal depressed, start the engine.
As the engine starts, the brake pedal should move slowly toward the floor. If the pedal height does not change, the vacuum booster assembly is faulty.
NOTE: If a faulty part is detected after inspection, check precisely with measuring devices.

LOADED AIR TIGHTNESS CHECK

Depress the brake pedal while the engine is running, and turn the engine to OFF while the pedal is depressed.

Keep the pedal depressed for 30 seconds. If the pedal height does not change, the function of vacuum booster assembly is normal. If the pedal height increases, it is faulty.

NOTE: If a faulty part is detected after inspection, check precisely with measuring devices.