Circuit Description
P0441 - VSV for EVAP is used to purge evaporative emissions from fuel tank into intake manifold. Also, it creates a vacuum inside fuel tank together with operation of VSV for Canister Closed Valve (CCV) and leak tests are performed using this vacuum. When VSV for EVAP remains open (opened malfunction), vacuum inside fuel tank does not change. When VSV for EVAP remains open (opened malfunction), vacuum inside fuel tank changes according to operation of VSV for CCV. DTC is set when pressure in charcoal canister and fuel tank does not drop during purge control or during purge cut-off, negative pressure coming into charcoal canister and fuel tank will not stop (2 trip detection logic).
P0446 - VSV for CCV is open under normal conditions. When VSV for EVAP is used to purge evaporative emissions from fuel tank into intake manifold, air is drawn from charcoal canister into fuel tank. Also, VSV for CCV has a function that relieves pressure in case pressure inside fuel tank has rapidly increased. Also, it creates a vacuum inside fuel tank in unison with operation of VSV for EVAP, and leak tests are performed using this vacuum. When VSV for CCV remains closed (closed malfunction), vacuum created inside fuel tank cannot be relieved. When VSV for CCV remains open (opened malfunction), it cannot create a large vacuum. DTC is set when VSV for CCV is on and pressure in charcoal canister and fuel tank is maintained at atmospheric pressure (2 trip detection logic).
P0442, P0456 - Vapor pressure sensor, VSV for EVAP and VSV for CCV are used to detect abnormalities in evaporative emission control system. ECM judges whether abnormalities exist in evaporative emission control system, based on signals from vapor pressure sensor. If evaporative emissions leak from components specified within the dotted line or vapor pressure sensor malfunctions, ECM records DTC P0442 or P0456. See Fig 1. DTC is set after cold engine start and after VSV for EVAP operation, VSV for EVAP is turned off sealing vacuum in system and ECM begins to monitor pressure increase. Some increase is normal. A very rapid, sharp increase in pressure indicates a leak in EVAP system and sets DTC P0442. This monitoring method is also able to distinguish between a small and a very small leak (DTC P0456). A pressure rise just above normal indicates a very small hole (2 trip detection logic).
Possible causes are:
- Disconnected, cracked, leaking or blocked vacuum hose.
- Fuel tank cap incorrectly installed or damaged.
- Vapor pressure sensor circuit is open or shorted.
- Defective vapor pressure sensor.
- EVAP VSV circuit is open or shorted.
- Defective EVAP VSV.
- Vapor pressure sensor VSV circuit is open or shorted.
- Defective vapor pressure sensor VSV.
- Defective charcoal canister.
- Defective fuel tank.
- Defective over fill check valve.
- Charcoal canister cracked, holed or otherwise damaged.
- Defective ECM.