37. A vacuum boost system shall have enough power in reserve for 3 assisted service brake applications while the engine is off. If the system has a warning light or buzzer, it shall operate where the vacuum is less than 2 kPa.
In the absence of a manometer, the vacuum shall be sufficient for an assisted braking when the warning device comes on.
A vacuum pump shall be capable of providing and maintaining a minimum vacuum of 4.5 kPa.