Park the vehicle on a level surface. Place the vehicle in PARK (automatic) or REVERSE (manual) with the engine OFF, and apply the parking brake. Chock the rear wheels to prevent vehicle movement.
NOTE: Wheel chocks may be purchased at your local auto parts store, or a block of wood cut into wedges may be used.
Start the vehicle and operate the engine at idle without touching the brake pedal for at least one minute.
NOTE: For manual transmission vehicles, place the vehicle in NEUTRAL with the parking brake applied.
Turn off the engine and wait one minute.
Test for the presence of assist vacuum by depressing the brake pedal and releasing it several times. If vacuum is present in the system, light application will produce less and less pedal travel. If there is no vacuum, there is a leak allowing air into the system.
