Circuit Description
For leak check, vacuum switching valve (VSV) malfunction condition, DTC detection timing and fuel tank pressure diagrams, see Fig 1 and Fig 2 .
DTC P0441: The VSV for evaporative emission control (EVAP) is used to purge the evaporative emissions from the fuel tank into the intake manifold. Also, it creates a vacuum inside the fuel tank in unison with the operation of the VSV for canister closed valve (CCV) and leak tests are performed using this vacuum. When the VSV for EVAP remains closed (closed malfunction), the vacuum inside the fuel tank does not change. When the VSV for EVAP remains open (open malfunction), the vacuum inside the fuel tank changes according to the operation of the VSV for CCV.
Detecting condition is when pressure in charcoal canister and fuel tank does not drop during purge control (2 trip detection logic) or negative pressure incoming in the charcoal canister and fuel tank will not stop during purge cut-off (2 trip detection logic).
DTC P0446: The VSV for CCV is open under normal conditions. When the VSV for EVAP is used to purge the evaporative emissions from the fuel tank into the intake manifold, air is drawn from the fuel tank into the charcoal canister. Also, the VSV for CCV has a function that relieves the pressure when the pressure inside the fuel tank has rapidly increased. Also, it creates a vacuum inside the fuel tank in unison with the operation of the VSV for EVAP and leak tests are performed using this vacuum.
When the VSV for CCV remains closed (closed malfunction), the vacuum created inside the fuel tank cannot be relieved. When the VSV for CCV remains open (open malfunction), it cannot create a large vacuum.
Detecting condition is when VSV for CCV is ON, pressure in charcoal canister and fuel tank is maintained at atmospheric pressure (2 trip detection logic).
DTCs P0442 & P0456: The vapor pressure sensor, VSV for EVAP and VSV for CCV are used to detect abnormalities in the evaporative emission control system. The ECM judges whether or not abnormalities exist in the evaporative emission control system, based on the signals from the vapor pressure sensor. The ECM records DTCs P0442 or P0456 if evaporative emissions leak from the components specified within the dotted line, see Fig 3, or the vapor pressure sensor malfunctions.
After a cold engine start, detecting condition is when after VSV for EVAP operation, the VSV for EVAP is turned off sealing the vacuum in the system and the ECM begins to monitor the pressure increase. Some increase is normal. A very rapid, sharp increase in pressure indicates a leak in the EVAP system and sets the DTC P0442. This monitoring method is also able to distinguish what is called the small or very small leak detection (DTC P0456). A pressure rise just above normal indicates a very small hole (2 trip detection logic).