Loaded Air Tightness Check

Start the engine and depress the brake pedal with a pedal force of 196 N (20 kgf, 44 Ibf).
Keep the engine running at idle and the pedal depressed until vacuum pressure of the vacuum gauge indicates 93 kPa (697 mmHg, 27.47 inHg).

Courtesy of SUBARU OF AMERICA, INC.
Stop the engine and check the vacuum gauge.
If the value matches the following standard, the vacuum booster assembly function is normal.

Vacuum pressure: standard

The range of vacuum pressure drop within 15 seconds after stopping the engine is 3.3 kPa (25 mmHg, 0.98 inHg) or less

If a faulty part is detected after inspection, refer to "AIR TIGHTNESS CHECK". Ref. to BRAKE>BRAKE BOOSTER>INSPECTION .
If the vacuum booster assembly is faulty, replace it with a new part.