Air Tightness Check

1. Start the engine and keep it running until a vacuum of 66.7 kPa (500 mmHg, 19.69 inHg) = point A is indicated on vacuum gauge. Do not depress the brake pedal at this moment.
   Fig 1: Air Tightness Checking Connection Diagram

   Courtesy of SUBARU OF AMERICA, INC.
2. Stop the engine and watch the gauge. If the vacuum drop range is less than 3.3 kPa (25 mmHg, 0.98 inHg) within 15 seconds after stopping the engine, brake booster is functioning properly.

If defective, the cause may be one of those listed below.

• Check valve malfunction
• Leak from vacuum hose
• Leak from shell jointed portion or stud bolt welded portion
• Damaged diaphragm
• Leak from valve body seal and bearing portion
• Leak from plate and seal assembly portion
• Leak from poppet valve assembly portion