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 600 RPM there should be at least -135 mbar (-1.96 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 above 220 mbar (3.19 psi) for 10 seconds or engine off vehicle speed present and low booster vacuum present.