Circuit Description
The vapor pressure sensor, VSV for EVAP, VSV for canister closed valve (CCV) and VSV for pressure switching valve are used to detect abnormalities in the evaporative emission control system. The ECM decides whether there is an abnormality in the evaporative emission control system based on the vapor pressure sensor signal. DTCs P0442 or P0456 is recorded by the ECM when evaporative emissions leak from the components within dotted line shown in illustration or when the vapor pressure sensor malfunctions. See Fig 1 (a).
After purge operation, the VSV for EVAP is turned off sealing the vacuum in the system and the ECM begins to monitor the pressure increase. It is a normal if the increase in pressure is lower than the predict level. See Fig 1 (b). A very rapid, sharp increase in pressure indicates a leak in the EVAP system and sets the DTC P0442. A pressure rise just above normal indicates a very small hole and will set the DTC P0456.