Fix P0446: Mechanic’s solutions that WORKED

P0446 Evaporative Emission Control System Vent Circuit Malfunctionsays there is something off with the Evaporative Emission Control System. This hiccup is often due to the Canister Close Valve (CCV).

Picture it as the guardian of your car’s emissions, and if it’s acting up, the system might get a little leaky. We’ll break down why this code shows up and how the CCV swoops in as the troubleshooter.

P0446 quick overview

Meaning	Evaporative Emission Control System Vent Control Circuit Malfunction
Is it serious?	EVAP codes should be addresed right away and fixed ASAP
What is EVAP?	– The EVAP system prevents fuel vapors from escaping into the atmosphere – It includes components like the charcoal canister, purge valve, and vent control valve
Possible causes	Faulty vent control valve Damaged or disconnected hoses in the EVAP system Faulty charcoal canister Wiring or electrical issues in the vent control circuit Issues with the fuel tank pressure sensor
Diagnostic steps	1. Check Gas Cap: Ensure the gas cap is tightly sealed, as a loose cap can trigger the code. 2. Inspect EVAP System Components: Visually inspect hoses, charcoal canisters, and related components for damage or disconnection. 3. Check Wiring and Connectors: Inspect wiring and connectors in the vent control circuit for damage or corrosion. 4. Test Vent Control Valve: Test the vent control valve for proper operation. 5. Check Fuel Tank Pressure Sensor: Verify the functionality of the fuel tank pressure sensor.
Common fixes	– Tightening or replacing the gas cap – Repairing or replacing damaged hoses in the EVAP system – Replacing a faulty vent control valve – Addressing wiring or connector issues – Replacing a malfunctioning fuel tank pressure sensor – Replace EVAP canister

How to fix P0446 – learn from mechanics

I looked into P0446 service cases at iatn.com website where in the private forums the mechanics seek advice from other mechanics. I looked up a bunch of cases to help you decide how to fix your issue and see what would a real mechanic do to solve it.

Case #1: Toyota

Vehicle Information:
1999 Toyota Camry CE 2.2L

Issue + Repair History:

• The MIL (Malfunction Indicator Lamp) was illuminated with code P0446 (Evaporative Emission Control System Vent Control Circuit Malfunction).
• The vehicle was acquired from another shop that had attempted to address the P0446 code by replacing sensors.
• An EVAP sensor was replaced, and a TSB modification for P0446 was performed without success.

Suggestions from the Community:

• Multiple suggestions to check the gas cap for proper sealing.
• Numerous recommendations to replace the EVAP canister assembly.
• Advice to inspect the vent valve in the canister for potential issues, including checking for black dust or pebbles when unplugging the vent valve.
• Consideration of the vacuum switching valve (VSV) on the canister as a common culprit.

Final Fix:
Following advice from the iATN community, replacing the EVAP canister assembly resolved the issue.

Case #2: Nissan

Vehicle Information:
1997 Nissan Sentra GLE 1.6L

Issue + Repair History:

• The MIL (Malfunction Indicator Lamp) was on with codes P0440 (Evap Control Valve) and P0446 (Evap Vent Problem).
• The vehicle was acquired from another shop that had attempted to address the P0446 code by replacing sensors.
• The EVAP sensor was replaced, and a TSB modification for P0446 was performed without success.

Diagnostic Steps:

• Replaced the stuck Evap Vent Control Valve and canister to address P0440.
• Continued issue with P0446 despite initial fixes.
• Checked power to vent control valve (12V), continuity to sensors, and various components related to the EVAP system.
• Verified normal operation of activated sensors.
• Applied vacuum to the EVAP Pressure Sensor, observed fluctuations, and replaced it with part #25085-3M201.

TSB Bulletin Utilized:

• TSB #NTB97-027 addressed MIL ON DTC P0440, P0443, or P0446 stored due to EVAP system pressure sensor.
• Replaced the EVAP Vent Control Valve to resolve P0440.
• Followed TSB guidance to check and replace the EVAP Pressure Sensor.

Final Fix:
Replacing the EVAP pressure sensor and the stuck EVAP vent control valve fixed all the issues, and the code did not return.

Case #3: Hyundai

Vehicle Information:
2003 Hyundai Santa Fe LX 3.5L

Issue + Repair History:

• The P0446 code was pending only on startup; the MIL (Check Engine Light) came on during the second startup, not during a road test.
• The fuel tank pressure sensor and vent valve were previously replaced.

Suggestions from the Community:

• Suggested replacing the charcoal canister based on experience with Toyota vehicles.
• Advised checking for an open circuit in the vent valve and examining the wiring from the PCM to the valve.
• Recommended correcting misinformation about P0446 being invalid for Hyundai and checking and possibly replacing the canister close valve.
• Emphasized the importance of checking the air filter and hose attached to the canister close valve for restrictions.
• Provided a detailed diagnostic guide, focusing on checking the canister close valve, charcoal canister, and related components.
• Mentioned the tendency for dirt on the face of the close canister valve and recommended replacing both the valve and charcoal canister.
• Pointed out that the purge control solenoid valve is a likely culprit for the P0446 code, providing troubleshooting information.

Final Fix:
The issue was fixed by replacing the EVAP canister and canister close valve.