Freeze Frame
OBD-II trouble code

P0446

Evaporative Emission System Vent Control Circuit

Severity Moderate Driving See conditions below System EVAP ventilation and control Applies to OBD-II gasoline vehicles using an evaporative-emissions vent monitor

Published · Reviewed and updated

In plain English: The EVAP vent check failed. Depending on the vehicle, investigate an electrical fault or restricted venting before buying a valve.

A short trip may be possible with normal running and no fuel odor or leakage. Arrange prompt diagnosis. Stop for strong fuel odor, visible fuel, repeated stalling, severe rough running or a flashing check-engine light. Keep ignition sources away from suspected fuel leaks.

A diagnostic starting point: Damaged vent hoses, filters or connectors. Start by asking: Is this vehicle testing a circuit or vent performance? Illustrative parts budgets span $10–$1000 USD, with diagnosis, labor and taxes extra.

Quick answers about P0446

What does P0446 mean?
The EVAP vent check failed. Depending on the vehicle, investigate an electrical fault or restricted venting before buying a valve.
What should I check first for P0446?
One starting point is Damaged vent hoses, filters or connectors. Inspect for blockage, water, corrosion and disturbed routing. Match the next test to the vehicle's monitor. The code alone does not identify a failed part; follow the procedure for your vehicle.
Can I drive with P0446?
A short trip may be possible with normal running and no fuel odor or leakage. Arrange prompt diagnosis. Stop for strong fuel odor, visible fuel, repeated stalling, severe rough running or a flashing check-engine light. Keep ignition sources away from suspected fuel leaks.
How much does it cost to fix P0446?
Illustrative parts budgets in this guide span $10–$1000 USD. Diagnosis, labor and taxes are extra. Price the demonstrated repair. The code name cannot tell you whether this job needs a hose, wiring repair, valve or a larger assembly.
How do I diagnose P0446?
Start with: Is this vehicle testing a circuit or vent performance? Save all codes and freeze-frame information. Look up the exact definition and related bulletin coverage. Note fuel level, temperature and recent repairs. Decide whether the next measurement is electrical behavior, pressure response or both. Do not assume a generic scan-tool label describes the complete manufacturer test.

Watch the P0446 videos

Full diagnostic video · 10:49 YouTube Short · 1:03

Full walkthrough — 10:49. Watch on YouTube

What P0446 actually means

The charcoal canister stores fuel vapor. Its vent path allows air exchange, while a controlled valve can seal that path for testing. The engine computer checks electrical behavior or the resulting pressure response, depending on the design. A command on a scanner tells you what the computer requested. It does not prove that a wire carried current or a valve allowed air through.

P0446 is often labeled vent control circuit, but the manufacturer's definition matters. One Mitsubishi design checks the solenoid's electrical response. GM applications can use this code for vent-system performance. Other designs check pressure changes across several valves. There is no universal resistance value, pressure threshold, valve state or test time for every P0446 vehicle.

Illustrative vent path — layout varies Fuel tank Vapor space Pressure feedback where fitted Charcoal canister Vent valve Verify actual state Filter Atmosphere Fresh-air path Feedback signal ECM vent command Electrical control P0446: electrical circuit or vent-performance fault, depending on the manufacturer. A command does not prove actual airflow. Check the circuit and the vent path.
Schematic illustration; the vehicle's layout may differ. Identify the monitor, then prove electrical control and vent flow.

Symptoms

Possible causes and what to check

This is a practical diagnostic order, not measured failure rates. Follow the tests and priorities specified for your vehicle; a code alone does not identify a failed part.

1 Damaged vent hoses, filters or connectors
Inspect for blockage, water, corrosion and disturbed routing. Match the next test to the vehicle's monitor.
2 Vent valve that sticks or fails its electrical test
Check both the required electrical response and the mechanical function. A click alone cannot prove unrestricted flow or sealing.
3 Missing power or a damaged control circuit
Use the correct wiring diagram and approved circuit tests. A replacement valve cannot restore a broken feed or control wire.
4 Restricted canister or fresh-air inlet
Debris, water or an obstructed inlet can impair venting. Isolate the affected section before replacing the canister assembly.
5 Pressure feedback or sensor-reference problem
On pressure-based monitors, verify the reading and its reference. Some application-specific faults distort feedback without a blocked vent valve.
6 Other valve, test-condition or controller issue
Check the full system layout and applicable bulletins. Consider a controller only after its circuits and inputs have passed the specified checks.

Illustrative vent-release test: does vacuum decrease?

Illustrative graph, not a recording from your vehicle or a universal service limit. Confirm the test conditions, units and acceptance criteria in the applicable service procedure.

This graph illustrates a pressure-based vent-release test. It does not represent every P0446 monitor.

In this invented example, the monitored vapor space begins under a small vacuum. Purge is closed, the vent is requested open, and the remaining valves are in the required states. Zero gauge pressure means atmospheric pressure here. These numbers explain the pattern; they are not a service limit or a direction to apply this vacuum to your car.

-0.8 -0.6 -0.4 -0.2 0.0 0.2 0 4 8 12 16 20 EVAP pressure (kPa gauge; illustrative) Seconds after the specified vent-open request Vacuum releases - illustrative Vacuum remains - illustrative
Vent-release example: validate the pressure signal. Slow release: inspect the path and valve operation.

The green line rises toward zero as the vacuum decreases. Air can reach the monitored space in this example. Use the exact procedure to judge the rate and final reading. An unrelated leak can also change pressure, so a rising line alone does not prove the entire EVAP system is healthy.

The red line stays below zero. Investigate a restricted path or incorrect valve operation, but first confirm the pressure signal. A sensor-reference obstruction, continued purge or a different isolation-valve state can change the result. This trace cannot identify which component to buy, and it cannot replace an electrical circuit test.

A slow vacuum release can mean a restriction or misleading feedback. Check the whole vent path and the vehicle-specific procedure; do not condemn the valve from this graph alone.

How to diagnose it, in order

  1. Is this vehicle testing a circuit or vent performance?
    Save all codes and freeze-frame information. Look up the exact definition and related bulletin coverage. Note fuel level, temperature and recent repairs. Decide whether the next measurement is electrical behavior, pressure response or both. Do not assume a generic scan-tool label describes the complete manufacturer test.
    Then → step 2
  2. Are the vent path and connections free of visible defects?
    With the vehicle safely supported and ignition off, inspect accessible hoses, the filter, inlet and wiring. Look for a pinched line, debris, water intrusion, corrosion or a disconnected plug. Check applicable routing updates. Do not remove a filter permanently or leave the cap loose as a workaround.
    Yes → go to step 3
    No → Repair the demonstrated defect, then retest
  3. Does vent-valve control pass the prescribed tests?
    A suitable bidirectional scan tool may operate the valve. Follow the circuit diagram to check power, connections, control and the solenoid as specified. Identify whether an energized valve opens or closes on this vehicle. Do not apply arbitrary battery power, bridge a fuse or use a heavy test load on a computer driver.
    Yes → go to step 4
    No → Repair the verified circuit fault or proven bad valve
  4. Do actual vent flow and pressure feedback pass?
    When required, validate sensor baseline and response before trusting the graph. Isolate the vent line, filter, valve and canister using the approved flow or pressure method. Check purge and other valves too. A smoke check may help with leaks but does not prove unrestricted airflow. Use approved low-pressure EVAP equipment with the engine off, away from ignition sources, and the specified inert gas. Never mouth-test vapor parts.
    Yes → go to step 5
    No → Correct the proven restriction, valve or feedback problem
  5. Does the repaired system pass its completed monitor?
    Repeat the failed functional check and the specified monitor conditions. Confirm refueling concerns are resolved when they were part of the complaint. An intermittent cold-weather fault may need its original conditions to be reproduced. A GM bulletin for certain Colorado and Canyon models describes water or ice at the pressure-sensor reference; it does not justify replacing every vent valve or pressure sensor.
    Yes → Retain the passing results and confirm symptoms are resolved
    No → Continue the application-specific diagnosis

Confirm the fault is resolved and the monitor completes. Clearing the light alone does not verify the repair.

What you need to do this yourself

Some links may be affiliate links. They cost you nothing extra and do not change which tools are recommended — the diagnostic order on this site is the same either way.

Illustrative repair budgets

These are rough US planning examples, not shop quotes or measured repair averages. Parts and labor are separate. Diagnosis, taxes, difficult access and additional repairs can increase the total. Some verified restrictions need cleaning by an approved procedure rather than a replacement assembly.

Illustrative budgets in USD; labor time is shown separately
RepairParts (USD)Labor time
Accessible hose, filter or connector repair
Identify the damaged or restricted section before ordering parts.
 $10–$150 1.0 h
Standalone vent valve
Prove its fault and check why it failed. Integrated designs can cost more.
 $30–$300 1.0 h
Vent-pipe or filter relocation assembly
Use an applicable service update, not improvised plumbing.
 $40–$400 1.5 h
Pressure sensor or sensor assembly
Separate a failed sensor from a blocked reference or wiring defect.
 $40–$400 2.0 h
Canister or integrated vent assembly
Replace only after isolating the fault and addressing contamination.
 $120–$1000 2.5 h

Price the demonstrated repair. The code name cannot tell you whether this job needs a hose, wiring repair, valve or a larger assembly.

P0446 video summary · 1:03

A brief introduction to the code and a diagnostic starting point. Use the full guide and vehicle-specific service information for the complete procedure.

Watch this Short on YouTube

Written diagnostic walkthrough

Current written guidance organized by topic. This text may include corrections made after a video was published and is not a verbatim transcript of the archived video.

Meaning and driving guidance

Code P0446. Evaporative Emission System Vent Control Circuit.

In plain English: the EVAP vent check failed. Depending on the vehicle, investigate an electrical fault or restricted venting before buying a valve.

A short trip may be possible with normal running and no fuel odor or leakage. Arrange prompt diagnosis. Stop for strong fuel odor, visible fuel, repeated stalling, severe rough running or a flashing check-engine light. Keep ignition sources away from suspected fuel leaks.

How it is measured

Here's what your engine computer is actually measuring.

The charcoal canister stores fuel vapor. Its vent path allows air exchange, while a controlled valve can seal that path for testing. The engine computer checks electrical behavior or the resulting pressure response, depending on the design. A command on a scanner tells you what the computer requested. It does not prove that a wire carried current or a valve allowed air through.

P0446 is often labeled vent control circuit, but the manufacturer's definition matters. One Mitsubishi design checks the solenoid's electrical response. GM applications can use this code for vent-system performance. Other designs check pressure changes across several valves. There is no universal resistance value, pressure threshold, valve state or test time for every P0446 vehicle.

A restricted vent, an electrical defect and a misleading pressure reading require different repairs. P0446 alone cannot distinguish them, and it is not a measured leak-size code.

Symptoms

What you'll usually notice, beyond the light itself.

Check-engine light with normal driving. The failed monitor may be the only obvious symptom. Save the diagnostic record before clearing it.

Repeated fuel-nozzle shutoff on some vehicles. Restricted venting can make refueling difficult. Do not keep forcing fuel into the tank; investigate the cause.

Intermittent faults after dust, water or freezing weather. Environmental clues can help reproduce a restriction or connection problem. They are not proof that one particular component failed.

Related vent, pressure or EVAP codes. Read the complete code list. Fuel odor, leakage or severe running problems need attention even if this vent code is also present.

Possible causes

Here is a practical order for checking the possible causes. These are diagnostic priorities, not measured failure rates.

Check 1: Damaged vent hoses, filters or connectors. Inspect for blockage, water, corrosion and disturbed routing. Match the next test to the vehicle's monitor.

Check 2: Vent valve that sticks or fails its electrical test. Check both the required electrical response and the mechanical function. A click alone cannot prove unrestricted flow or sealing.

Check 3: Missing power or a damaged control circuit. Use the correct wiring diagram and approved circuit tests. A replacement valve cannot restore a broken feed or control wire.

Check 4: Restricted canister or fresh-air inlet. Debris, water or an obstructed inlet can impair venting. Isolate the affected section before replacing the canister assembly.

Check 5: Pressure feedback or sensor-reference problem. On pressure-based monitors, verify the reading and its reference. Some application-specific faults distort feedback without a blocked vent valve.

Check 6: Other valve, test-condition or controller issue. Check the full system layout and applicable bulletins. Consider a controller only after its circuits and inputs have passed the specified checks.

Use the test results to choose the repair. A position in this list does not prove that a part has failed.

Illustrative diagnostic pattern

This graph illustrates a pressure-based vent-release test. It does not represent every P0446 monitor.

In this invented example, the monitored vapor space begins under a small vacuum. Purge is closed, the vent is requested open, and the remaining valves are in the required states. Zero gauge pressure means atmospheric pressure here. These numbers explain the pattern; they are not a service limit or a direction to apply this vacuum to your car.

The green line rises toward zero as the vacuum decreases. Air can reach the monitored space in this example. Use the exact procedure to judge the rate and final reading. An unrelated leak can also change pressure, so a rising line alone does not prove the entire EVAP system is healthy.

The red line stays below zero. Investigate a restricted path or incorrect valve operation, but first confirm the pressure signal. A sensor-reference obstruction, continued purge or a different isolation-valve state can change the result. This trace cannot identify which component to buy, and it cannot replace an electrical circuit test.

A slow vacuum release can mean a restriction or misleading feedback. Check the whole vent path and the vehicle-specific procedure; do not condemn the valve from this graph alone.

Diagnostic steps

Use the exact model and engine procedure to choose the branch. This sequence is a guide to gathering evidence, not a substitute for factory specifications.

Step 1. Is this vehicle testing a circuit or vent performance? Save all codes and freeze-frame information. Look up the exact definition and related bulletin coverage. Note fuel level, temperature and recent repairs. Decide whether the next measurement is electrical behavior, pressure response or both. Do not assume a generic scan-tool label describes the complete manufacturer test.

Step 2. Are the vent path and connections free of visible defects? With the vehicle safely supported and ignition off, inspect accessible hoses, the filter, inlet and wiring. Look for a pinched line, debris, water intrusion, corrosion or a disconnected plug. Check applicable routing updates. Do not remove a filter permanently or leave the cap loose as a workaround.

Step 3. Does vent-valve control pass the prescribed tests? A suitable bidirectional scan tool may operate the valve. Follow the circuit diagram to check power, connections, control and the solenoid as specified. Identify whether an energized valve opens or closes on this vehicle. Do not apply arbitrary battery power, bridge a fuse or use a heavy test load on a computer driver.

Step 4. Do actual vent flow and pressure feedback pass? When required, validate sensor baseline and response before trusting the graph. Isolate the vent line, filter, valve and canister using the approved flow or pressure method. Check purge and other valves too. A smoke check may help with leaks but does not prove unrestricted airflow. Use approved low-pressure EVAP equipment with the engine off, away from ignition sources, and the specified inert gas. Never mouth-test vapor parts.

Step 5. Does the repaired system pass its completed monitor? Repeat the failed functional check and the specified monitor conditions. Confirm refueling concerns are resolved when they were part of the complaint. An intermittent cold-weather fault may need its original conditions to be reproduced. A GM bulletin for certain Colorado and Canyon models describes water or ice at the pressure-sensor reference; it does not justify replacing every vent valve or pressure sensor.

Confirm the fault is resolved and the monitor completes. Clearing the light alone does not verify the repair.

Illustrative repair budgets

These are rough US planning examples, not shop quotes or measured repair averages. Parts and labor are separate. Diagnosis, taxes, difficult access and additional repairs can increase the total. Some verified restrictions need cleaning by an approved procedure rather than a replacement assembly.

Accessible hose, filter or connector repair: 10 to 150 dollars in parts, plus about 1.0 hours of labor. Identify the damaged or restricted section before ordering parts.

Standalone vent valve: 30 to 300 dollars in parts, plus about 1.0 hours of labor. Prove its fault and check why it failed. Integrated designs can cost more.

Vent-pipe or filter relocation assembly: 40 to 400 dollars in parts, plus about 1.5 hours of labor. Use an applicable service update, not improvised plumbing.

Pressure sensor or sensor assembly: 40 to 400 dollars in parts, plus about 2.0 hours of labor. Separate a failed sensor from a blocked reference or wiring defect.

Canister or integrated vent assembly: 120 to 1000 dollars in parts, plus about 2.5 hours of labor. Replace only after isolating the fault and addressing contamination.

Price the demonstrated repair. The code name cannot tell you whether this job needs a hose, wiring repair, valve or a larger assembly.

Sources and application limits

These manufacturer documents and technical references support the discussion. A bulletin may apply only to its listed models, engines and production dates; confirm coverage before applying it.

P0441 P0449 P0451 P0456