Operation Check When Using Measuring Devices

WARNING: This page is about a different car, the 2015 Subaru Outback and 2015 Subaru Legacy. 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.

Check with measuring devices
Connect a measuring device as shown in the figure. After bleeding air from the pressure gauge, perform each check.

Fig 1: Checking Brake Booster Operation
Courtesy of SUBARU OF AMERICA, INC.
Air tightness check
1. Start the engine and keep it running at idle until vacuum pressure indicates 66.7 kPa (500 mmHg, 19.69 inHg) while the brake pedal is not depressed.
  
  Fig 2: Checking Air Tightness
  Courtesy of SUBARU OF AMERICA, INC.
2. Stop the engine and check the vacuum pressure.
  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, it may results from one of the following causes.
  - Check valve malfunction
  - Leak from vacuum hose
  - Leak from shell joint section or stud bolt welded section
  - Damaged diaphragm
  - Leak from valve body seal and bearing section
  - Leak from plate and seal assembly section
  - Leak from poppet valve assembly section
Loaded air tightness check
1. Start the engine and depress the brake pedal with a pedal force of 196 N (20 kgf, 44 lbf).
2. Keep the engine running at idle and the pedal depressed until vacuum pressure of the vacuum gauge indicates 66.7 kPa (500 mmHg, 19.69 inHg).
  
  Fig 3: Checking Loaded Air Tightness
  Courtesy of SUBARU OF AMERICA, INC.
3. Stop the engine and check the vacuum gauge.
  If the value matches the following standard, the vacuum booster 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 INSPECTION , Brake Booster.>
4. If the vacuum booster assembly is faulty, replace it with a new part.

Lack of boost action check

Turn the engine OFF, and set the value of the vacuum gauge to "0".

Check the fluid pressure when the brake pedal is depressed. The pressure must be greater than the specification listed.

Brake pedal force: N (kgf, lbf)	147 (15, 33)	294 (30, 66)
Fluid pressure: kPa (kgf/cm² , psi)	533 (5, 77)	1551 (16, 225)

Boosting action check

Set the vacuum gauge reading to 66.7 kPa (500 mmHg, 19.69 inHg) with the engine running.

Check the fluid pressure when the brake pedal is depressed. The pressure must be greater than the specification listed.

Brake pedal force: N (kgf, lbf)	147 (15, 33)	294 (30, 66)
Fluid pressure: kPa (kgf/cm² , psi)	6177 (63, 896)	11273 (115, 1635)