Subaru Legacy BN/BS (2015-2019) Owners Manual: Brake booster

If the brake booster does not operate as described in the following procedure, have it checked by your SUBARU dealer.

1.  With the engine off, depress the brake pedal several times, applying the same pedal force each time. The distance the pedal travels should not vary.
2.  With the brake pedal depressed, start the engine. The pedal should move slightly down to the floor.
3.  With the brake pedal depressed, stop the engine and keep the pedal depressed for 30 seconds. The pedal height should not change.
4.  Start the engine again and run for approximately 1 minute then turn it off.

   Depress the brake pedal several times to check the brake booster. The brake booster operates properly if the pedal stroke decreases with each depression.