Monitor Description

If the engine is started, the purge flow monitor operates. The purge flow monitor consists of two monitors. First monitoring is performed every time, and the second monitoring is performed as necessary.

• First monitoring

When the engine is running, and purge VSV is ON (Open), the ECM monitors the purge flow rate by measuring the variation of EVAP pressure. If the pressure variation exceeds the threshold value, the ECM initiates second monitoring.

Fig 1: Purge Valve, EVAP Pressure And Time Characteristics Graph

Courtesy of SUBARU OF AMERICA, INC.

• Second monitoring

The vent valve turns to ON (Closed) and EVAP pressure monitoring is carried out. If the pressure fluctuation exceeds the threshold, the ECM judges that the purge VSV is in the stuck close status and illuminates the MIL, and stores DTC P0441 (2 trip detection logic).

Fig 2: Purge Valve, EVAP Pressure, Vent Valve And Threshold Characteristics Graph

Courtesy of SUBARU OF AMERICA, INC.