A test apparatus for an evaporative emission system includes a source of pressure (positive or negative), a sensor for sensing the pressure generated in the evaporative emission system, and an ECU which controls the operation of the source of pressure and receives signals from the sensor reporting the pressure in the vehicle evaporative emission system over time. The ECU compares the sensed data with the stored data representing standard baseline sample vehicles without any leaks to determine the presence of a leak in the evaporative emission system.