Inspection Without Using Tester

WARNING: This page is about a different car, the 2014 Mitsubishi Outlander. However, it is still accessible from the selected car via links, so may be relevant.

Carry out the simplified brake booster operation check in the following procedure:
1. Run the engine for 1 to 2 minutes, and then stop. Depress the brake pedal with normal depression force. The result is judged as "Good" when the pedal stroke is great at the first depression, and becomes smaller as you repeat depressing the pedal. If the pedal stroke does not change, the result is judged as "No Good."
  
  Fig 1: Proper And Improper Brake Booster Operation
  Courtesy of MITSUBISHI MOTOR SALES OF AMERICA.
2. With the engine stopped, depress the brake pedal several times. Keep the brake pedal depressed and start the engine. At this time, when the pedal moves down slightly, the result is judged as "Good." The result is judged as "No Good" if the pedal does not move down.
  
  Fig 2: Depressing Brake Pedal Several Times (With Engine Stopped)
  Courtesy of MITSUBISHI MOTOR SALES OF AMERICA.
3. With the engine running, depress the brake pedal. Stop the engine in this condition. The result is judged as "Good" when the pedal height does not change for approximately 30 seconds. The result is judged as "No Good" if the pedal moves up.
The brake booster is judged as normal when the results of all the above checks are "Good."
When one or more of the above check results are "No Good", then the check valve, vacuum hose, or brake booster is suspected faulty.

Fig 3: Caution For Depressing Brake Pedal (With Engine Running)
Courtesy of MITSUBISHI MOTOR SALES OF AMERICA.