Brake Booster Operating Test

WARNING: This page is about a different variant/trim than selected.

For simple checking of the brake booster operation, carry out the following tests:
1. Run the engine for one or two minutes, and then stop it. If the pedal depresses fully the first time but gradually becomes higher when depressed succeeding times, the booster is operating properly. If the pedal height remains unchanged, the booster is defective. Go to Step 2.
  
  Fig 1: Identifying Correct Methods For Testing Brake Booster Operation (1 Of 3)
  Courtesy of MITSUBISHI MOTOR SALES OF AMERICA.
2. With the engine stopped, step on the brake pedal several times. Then step on the brake pedal and start the engine. If the pedal moves downward slightly, the booster is in good condition. If there is no change, the booster is defective. Go to Step 3.
  
  Fig 2: Identifying Correct Methods For Testing Brake Booster Operation (2 Of 3)
  Courtesy of MITSUBISHI MOTOR SALES OF AMERICA.
3. With the engine running, step on the brake pedal and then stop the engine. Hold the pedal depressed for 30 seconds. If the pedal height does not change, the booster is in good condition, if the pedal rises, the booster is defective.
Fig 3: Identifying Correct Methods For Testing Brake Booster Operation (3 Of 3)
Courtesy of MITSUBISHI MOTOR SALES OF AMERICA.
If the above three tests are okay, the booster is OK. If one of the above three tests is not okay, the check valve, vacuum hose, or booster is defective. Check the check valve (Refer to CHECK VALVE OPERATION CHECK .), vacuum hose for leaks, high volume engine vacuum applied to booster. Repair or replace as necessary. If these are OK, replace booster and repeat this test starting at Step 1.