Symptoms

- Engine Light ON (or Service Engine Soon Warning Light) - Possible a noticeable fuel odor caused by the release of fuel vapors

Possible Causes

- Missing Fuel cap - Incorrect fuel filler cap used - Fuel filler cap remains open or fails to close - Foreign matter caught in fuel filler cap - Incorrect fuel tank vacuum relief valve

When Detected

- When VSV for pressure switching valve is ON, ECM judges that there is no continuity between vapor pressure sensor, fuel tank and charcoal canister (2 trip detection logic)

Tech Notes

Before replacing any parts, try re-tight the gas cap and clearing the code. If the cap or cap seal is damage replaced cap and clear the code.

Description

The vapor pressure sensor, Voltage Solenoide Valve (VSV) for EVAP, Voltage Solenoide Valve (VSV) for canister closed valve (CCV) and Valve Solenoide Valve (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. Diagnostic Trouble Code (DTC) P0446 is recorded by the ECM when there is a malfunction in either the VSV for EVAP, the VSV for pressure switching valve, or in the vapor pressure sensor itself, or when evaporative emissions leak from the components within the dotted line in Fig. 1 below. The ECM closes the CCV and opens the VSV for pressure switching valve causing vacuum to increase in the entire EVAP system. The ECM continues to operate the VSV for EVAP until the vacuum is increased to a specified point at which time the ECM closes the VSV for EVAP. If the vacuum did not increase, or if the vacuum increased beyond the specified limit, the ECM judges the VSV for EVAP and related components to be faulty. Source: Toyota