Circuit Description

WARNING: This page is about a different car, the 2003 Lexus ES 300. However, it is still accessible from the selected car via links, so may be relevant.

Vapor pressure sensor, VSV for Canister Closed Valve (CCV) and VSV for pressure switching valve are used to detect abnormalities in evaporative emission control system. ECM decides whether there is an abnormality in evaporative emission control system based on vapor pressure sensor signal. DTCs P0442 or P0456 is recorded by ECM when evaporative emissions leak from components within dotted line or when the vapor pressure sensor malfunctions. See Figure.

After purge operation, VSV for EVAP is turned off, sealing vacuum in system, and ECM begins to monitor pressure increase. It is normal if increase in pressure is lower than predicted level. A very rapid, sharp increase in pressure indicates a small leak in EVAP system and sets DTC P0442. A pressure rise just above normal indicates a very small leak and will set DTC P0456.

Possible causes are:

Fuel tank cap incorrectly installed.
Fuel tank cap cracked or damaged.
Hose or tube cracked, holed, damaged or loose seal (3). See Figure.
Vacuum hose cracked, holed, blocked, damaged or disconnected.
Fuel tank cracked, holed or damaged.
Charcoal canister cracked, holed or damaged.
Vapor pressure sensor circuit is open or shorted.
Defective VSV for CCV.
Defective VSV for EVAP.
Defective VSV for pressure switching valve.
Defective vapor pressure sensor.
Fuel tank over fill check valve cracked or damaged.
Defective ECM.