P0446

DTC P0446 Evaporative Emission Control System Vent Control Circuit

CIRCUIT DESCRIPTION

DTC Detection Condition:

The vapor pressure sensor, canister closed valve (CCV), EVAP VSV and 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 P0441 and P0446 are recorded by the ECM when evaporative emissions leak from the components within the dotted line in Fig. 1, or when there is a malfunction in the CCV, EVAP VSV, pressure switching valve, or in the vapor pressure sensor itself.

HINT: Typical DTC output of each trouble part

MONITOR DESCRIPTION

P0446

Monitor Strategy:

Typical Enabling Conditions:

Typical Malfunction Thresholds:

Monitor Result (Mode 06 Data):

If there is a malfunction detected in the evaporative emission (EVAP) VSV, the canister closed valve (CCV) and the pressure switching valve; the ECM will illuminate the MIL and set a DTC.

This portion of the EVAP diagnosis checks the following EVAP system functions:
a. CCV stuck closed:
The ECM checks for a CCV "stuck closed" malfunction by commanding the CCV to open after an EVAP leak test. If the fuel tank pressure does not rise (lose vacuum), the ECM determines that the CCV is stuck closed. The ECM will turn on the MIL and a DTC is set.
b. Pressure switching valve stuck closed:
The ECM checks for a pressure switching valve "stuck closed" malfunction by commanding the pressure switching valve to close after an EVAP leak test. If the fuel tank pressure does not change, the ECM determines that the pressure switching valve is malfunctioning. The ECM will turn on the MIL and a DTC is set.
c. CCV stuck open malfunction:
The ECM checks for the malfunction by signaling the VSV for EVAP to open with the CCV closed to create the negative pressure in the fuel tank. If the fuel tank does not develop an appropriate highly negative pressure, the ECM determines that the CCV is stuck open.

Wiring Diagram:

INSPECTION PROCEDURE

HINT:
- If DTC P0441 (Purge Flow), P0446 (VSV for CCV), P0451, P0452 or P0453 (Evaporative Pressure Sensor) is output with DTC P0442 or P0456, troubleshoot DTC P0441, P0446, P0451, P0452 or P0453 first. If no malfunction is detected, troubleshoot DTC P0442 or P0456 next.
- Read freeze frame data using the hand-held tester or the OBD II scan tool. Freeze frame data records the engine conditions when a malfunction is detected. When troubleshooting, freeze frame data can help determine if the vehicle was running or stopped, if the engine was warmed up or not, if the air-fuel ratio was lean or rich, and other data from the time the malfunction occurred.
- When the ENGINE RUN TIME in the freeze frame data is less than 200 seconds, carefully check the vapor pressure sensor.