Integrity diagnosis

Fig 1: Integrity Diagnosis - Control Module Communication Diagram

Courtesy of SAAB-SCANIA OF AMERICA, INC.

Fig 2: Integrity Diagnosis - Control Module Communication Circuit Diagram

Courtesy of SAAB-SCANIA OF AMERICA, INC.

The on-board diagnostics must be able to detect a leak in the purge system corresponding to a hole with diameter 1 mm.

For this reason, there is a differential pressure sensor fitted to the tank and a shut-off valve on the EVAP canister atmospheric connection. When the shut-off valve is closed, it should be possible to create and maintain a vacuum in the tank using the purge valve. Otherwise, the system is leaking and a diagnostic trouble code will be generated. The diagnosis is performed once per driving cycle.

The pressure sensor is powered with 5 V from control module pin 46 and grounded from control module pin 70. Depending on the pressure difference between the tank and the atmosphere, the pressure sensor will supply a proportional voltage to control module pin 59. The value from the pressure sensor is adapted to 0 kPa when the ignition is turned on, provided the engine coolant temperature is below 40°C and the fuel level is below 50 liters.

The shut-off valve is open in a de-energized state. It is powered from the main relay and is controlled from control module pin 37.