Brake Servo System

With the engine off, depress the brake pedal several times applying the same pedal force. Make sure the travel distance should not change.
With the brake pedal depressed, start the engine. Make sure the pedal should move slightly toward the floor.
With the brake pedal depressed, stop the engine and keep the pedal depressed for 30 seconds. Make sure the pedal height should not change.
A check valve is built into the vacuum hose. Disconnect the vacuum hose to inspect function of check valve.
Blow compressed air into vacuum hose from the end of brake booster side. Check that the air flows from the air hose on engine side. Next blow air into the hose from the engine side. Check that the air does not flow from the hose. Replace both of the check valve and vacuum hose if the check valve is faulty. Engine side of vacuum hose is indicated by marking "ENG" as shown.
- Non-turbo model
  
  Fig 1: Locating Check Valve And Vacuum Hose (Non-Turbo Model)
  Courtesy of SUBARU OF AMERICA, INC.
- Turbo model
  
  Fig 2: Locating Check Valve And Vacuum Hose (Turbo Model)
  Courtesy of SUBARU OF AMERICA, INC.
  
  Fig 3: Vacuum Hose Engine Side Marking
  Courtesy of SUBARU OF AMERICA, INC.
Check the vacuum hose for cracks or other damage.
CAUTION: When installing the vacuum hose on the engine and brake booster, do not use soapy water or lubricating oil on their connections.
Check the vacuum hose to make sure it is tightly secured.