Leak diagnosis
The on-board diagnosis must find a leak in the purge system corresponding to a hole of 0.5 mm diameter.
For this reason, a differential pressure sensor is mounted on the fuel pump cover and a shut-off valve for the atmospheric connection of the evaporative emission canister. When the shut-off valve is closed, a reduced pressure is created and maintained in the tank using the purge valve. Otherwise the system leaks, and a trouble code is set. Diagnosis is performed once per drive cycle.
The pressure sensor is supplied with 5V from the control unit pin 43(A), and grounded through control unit pin 32(A). Depending on the pressure difference between the tank and atmosphere, the pressure sensor gives a proportional voltage to control unit pin 11(A).
The shut-off valve is open in current less state. It is supplied from the main relay and controlled by control unit pin 2(B).