BRAKE BOOSTER OPERATION TEST WITHOUT A TESTER
For a simple check of brake booster operation, make the following tests.
Run the engine for one or two minutes, and then stop it. Depress the brake pedal several times at normal foot pressure. If the pedal goes down further at the first time, but gradually rises after the second or third time, the brake booster is functioning properly. Go to step 2.
With the engine stopped, depress the brake pedal several times. Depress the brake pedal and start the engine. If the pedal goes down slightly, the booster is in good condition. Go to step 3.
With the engine running, depress 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 one of the above three tests is not okay, check the vacuum hoses and the brake booster, make any necessary corrections. If all tests are OK, the unit is good