Theory Of Operation

When the Vacuum Pressure Sensor indicates a failure in the Vacuum Booster. After the cold start phase (i.e. 3 min after engine is running) and if the engine is running above 400 RPM there should be at least -200 mbar (-1.45 psi) of differential pressure in the vacuum-chamber for boosting the pedal force. If the pressure remains below this value for more than two minutes. Timer resets if the pressure remains below -200 mbar (-1.45 psi) for 10 seconds or engine is off with vehicle speed present and low booster vacuum present.