What does the P0446 Fault Code Mean and How to Fix?

What is the P0446 Fault Code?

The P0446 fault code is a common OBD-II diagnostic code, standing for EVAP System Vent Control Circuit Malfunction.In the previous article, we introduced the signs of EVAP system failure. Today, we will mainly explain the fault code P0446 and see which part of the EVAP system failure it is related to.

The EVAP system (evaporative emissions control system) prevents fuel vapor from being released directly into the atmosphere. Instead, it stores it in an activated charcoal canister and then, at the appropriate time, directs it through a purge valve into the intake manifold for combustion.

When the engine control module (ECM/ECU) detects abnormal voltage in the EVAP vent valve circuit, unexpected switch operation, or a clogged line, the P0446 fault code is triggered, and the engine check light illuminates.The P0446 code can often be diagnosed with an Autel scanner.

The P0446 fault code was detected using Autel AL619.

Typical Symptoms of the P0446 Trouble Code

Although the P0446 fault code doesn't severely affect engine operation like ignition or fuel injection system failures, it can still cause some noticeable symptoms:

• The Check Engine Light illuminates: This is the most immediate symptom.
• A odor of fuel vapor is present at the rear of the vehicle or near the fuel tank: This is especially noticeable after refueling.
• Failed exhaust gas tests: Due to a malfunction in the EVAP system, exhaust emissions may contain excessive hydrocarbons (HC).
• Slightly increased fuel consumption: Fuel vapor is not being effectively recovered.
• In some cases: unstable idle speed or a slight decrease in power

When the check engine light comes on, you need to use an Autel scanner to detect the P0446 code.

Many owners find that their vehicles still drive normally. However, if the P0446 fault code is not addressed for a long time, it may lead to fuel vapor leaks, excessive emissions, and even failure of the annual inspection.

Common Causes of the P0446 Fault Code

• EVAP Ventilation Control Valve Malfunction (Most Common): Coil burnout, seizure, or internal blockage.
• Activated Carbon Canister Clogged or Damaged: Carbon particles leaking and blocking the line.
• Ventilation Pipe Clogged or Bent: Resulting in abnormal vapor flow.
• Electrical issues: Poor Electrical Contact, Short Circuit, or Open Circuit
• Purge Valve Malfunction: Failure to open properly, affecting system balance.
• Fuel Tank Pressure Sensor Malfunction: The ECM receives an erroneous signal.
• ECM Program Error: rare cases

A bad vent valve can cause the P0446 code to appear.

Diagnostic Steps for the P0446 Trouble Code

To diagnose P0446, we recommend using an Autel scanner or other auto diagnostic tools. The process is as follows:

• Step 1: Read the fault code

  Confirm whether P0446 is the only fault or is accompanied by other EVAP-related codes (such as P0440, P0441, or P0449).

• Step 2: Check the freeze frame data

  Understand the operating conditions when the fault occurred.

• Step 3: Perform an active test:

  Use the Autel scanner to control the EVAP vent valve to confirm normal operation.

• Step 4: Test the circuit:

  Use a multimeter to test voltage and resistance to check for opens or shorts.

• Step 5: Check the pipeline and activated carbon canister

  To see if there is any blockage, rupture or carbon particle leakage.

• Step 6: Smoke test

  A common method involves injecting smoke into the EVAP system to locate leaks.

• Step 7: Check the fuel tank pressure sensor

  Confirm that the data is within the normal range.

Diagnose EVAP system status with Autel scanner.

Solutions for P0446

Depending on the cause, solutions include:

• Replace a damaged EVAP vent valve
• Clean or replace the activated charcoal canister
• Inspect and repair the vent line
• Repair or replace the wiring harness and connector
• Replace the purge valve
• Replace the fuel tank pressure sensor
• Update or replace the ECM if necessary

After repairs are complete, use an OBD-II diagnostic tool to clear the fault code and conduct a road test to confirm that P0446 does not trigger again.

Repair Case Reference

Case 1: Toyota Camry

The owner reported that the check engine light was on. An Autel scanner read the code: P0446. During the active test, the vent valve did not respond. The owner ultimately determined that the vent valve coil was burned out. Replacement resolved the issue.

If you are having trouble identifying the components of the EVAP system during maintenance, you can refer to the following explanation video using the Toyota Camry as an example:

Case 2: Chevy Silverado

There was a noticeable gasoline odor from the rear of the vehicle, and the exhaust gas emissions failed the annual inspection. Using an Autel scanner to read the fault codes revealed P0446 and P0442. Further inspection revealed a ruptured activated charcoal canister and carbon particles blocking the pipes.

The canister and pipes were replaced, and after clearing the fault codes, the problem was completely resolved.

Case 3: Honda Accord

The owner complained about increased fuel consumption. The fault code read: P0446. Inspection revealed a bend in the pipe, preventing vapor from venting. Reinstalling the pipe restored the problem.

Is it okay to drive with a P0446 code?

From a safety perspective, the vehicle can usually be driven after the P0446 fault occurs and will not break down in the short term. However:

• Long-term driving without repairs can lead to increased fuel consumption and environmental pollution;
• The vehicle may fail the annual exhaust gas test;
• Some models may experience excessive fuel tank pressure, posing a potential safety hazard.

Therefore, it is recommended to use an Autel scanner to locate the problem and repair it promptly.

The P0446 code may cause a failure in the annual emissions test.

How to Prevent the P0446 Fault?

• Do not frequently fill the tank to prevent liquid fuel from entering the activated charcoal canister.
• Regularly inspect the vent line to prevent aging or cracking.
• Use high-quality fuel to reduce sediment.
• Periodically scan with an OBD-II diagnostic tool to identify potential problems.

Summary

The P0446 fault code indicates an abnormality in the EVAP system ventilation control circuit and is common in Toyota, Honda, Chevrolet, Nissan, and other models. While it won't immediately cause a breakdown, it will trigger the fault light and affect emissions and fuel consumption.

Using the Autel scanner, technicians and vehicle owners can quickly read the code, perform proactive testing, and accurately locate the problem component, enabling efficient repairs.

Resolving P0446 promptly will not only restore your vehicle to normal performance, but will also prevent annual inspection failures and extend the life of the EVAP system.