P0446 EVAP vent control performance problem

EVAP vent valve or vent path restricted

Monitor

EVAP faults let fuel vapour escape but rarely change how the car drives, and the main risk is a failed emissions test, so it is safe to drive while you arrange a fix.

It gets more serious if:

  • Inspect soon: You keep smelling raw fuel around the car, not just right after filling up
  • Stop: You see liquid fuel dripping or pooling under the car, or near the filler, tank or canister

Source: how we rate severity

P0446 in short

P0446 means the EVAP vent valve, or the fresh-air path it controls, is not working as expected. The usual causes are a blocked vent hose or filter or a stuck vent valve, often from dust or a fuel-flooded canister. It is generally safe to drive unless you smell or see fuel.

The vent valve lets fresh air into the charcoal canister, and closes when the computer wants to seal the system for a leak test. It normally stays open and is closed by powering it.

If the computer commands the vent shut but sees no change, or sees a restriction when it should be open, it sets P0446. A kinked hose, a filter packed with dust or mud, or a canister soaked with liquid fuel can all restrict the vent.

P0449 is the electrical side of the same valve. If both are stored, check the wiring and connector first.

Most likely causes

These are general causes for this code across vehicles. None is specific to one make or model.

  1. Vent hose or vent filter blocked by dust, mud or debris

    Common general cause
    Why it ranks here
    Nissan names restricted vents as a common cause, and GM has a truck bulletin for P0446 caused by dust plugging the vent.
    What would change this
    Rises if air will not pass freely through the vent hose or the filter is packed with dirt.
    How to test the evap canister vent valve

  2. Vent valve stuck open or closed

    Common general cause
    Why it ranks here
    The valve itself is a moving part that is checked for its response, and it is the next most common failure.
    What would change this
    Rises if the valve does not respond when commanded with a scan tool.
    How to test the evap canister vent valve

  3. Canister flooded with liquid fuel, often from topping off

    Possible — needs testing
    Why it ranks here
    Topping off can push fuel into the canister and restrict the vent. Nissan says a heavy canister points to contamination.
    What would change this
    Rises if the canister is heavy or wet, or the owner often tops off the tank.
    How to test the evap charcoal canister

  4. Kinked or crushed vent hose

    Possible — needs testing
    Why it ranks here
    A pinched hose restricts the vent the same way debris does, but it is less common.
    What would change this
    Rises if you see a kink or crush mark along the vent hose.
    How to test the vacuum hoses and intake leaks

  5. Wiring or connector fault at the vent valve

    Possible — needs testing
    Why it ranks here
    The computer checks the circuit too, so a wiring fault more often sets P0449, but it can upset the performance test.
    What would change this
    Rises if P0449 is also stored.
    How to test the evap canister vent valve

What to test first

Start at step 1. Each result tells you what it means and where to go next.

  1. Read all stored and pending codes with a scan tool.

    Low riskTool: OBD-II scan tool

  2. With the engine off and cool, find the vent hose and filter near the canister or tank and look for kinks, crush damage, mud or dust packing.

    Use cautionTool: flashlight

    Warning:Fuel vapour is flammable. Work outdoors with the engine off and cool, and keep sparks, cigarettes and open flames away. Do not get under a car supported only by a jack.

  3. Disconnect the vent hose at the vent valve and check that air passes freely through the hose and filter.

    Use caution

    Warning:Fuel vapour is flammable. Work outdoors with the engine off and cool, and keep sparks, cigarettes and open flames away. Do not suck on any fuel system hose.

  4. Have a shop command the vent valve open and closed with a scan tool and check the canister.

    Best left to a shopTool: scan tool with output controls

    Warning:Shop test on the fuel vapour system.

Symptoms

  • Check engine light on, usually with no change in how the car drives
  • Fails an emissions or smog test because of the light or an incomplete EVAP monitor
  • Persistent raw fuel smell around the car Gets more serious: stop and have it checked.
  • Liquid fuel dripping under the car Gets more serious: stop and have it checked.

Compare with: Check engine light came on after getting gas

How to fix

  1. Stop filling once the pump clicks off the first time, so you do not flood the canister.

  2. If you can see the vent filter or hose end without lifting the car, check it for dust or mud.

    Warning:Engine off and cool. Do not get under a car supported only by a jack.

  3. After a repair, drive normally for several days so the monitor can re-run. Clearing codes or disconnecting the battery resets readiness, so do it shortly before an inspection only if you then complete a drive cycle.

Parts and cost context

  • EVAP canister vent valve:Usually mounted on or near the canister, close to the fuel tank. Labour varies, so get a quote.
  • EVAP charcoal canister:A canister flooded with fuel or shedding charcoal can damage new valves, so check it before replacing the valve alone.

Labor varies by vehicle and shop; get a quote before you approve a repair.

Compare used part prices on PartPriceGuide

On your vehicle

Chevrolet

  • 2019–2025 · Silverado 1500

    Supported by vehicle data

    GM bulletin 23-NA-073 links P0446, P0449, P0442 and P0455 on these trucks to dust plugging the canister and vent solenoid in very dusty use. Silverado 2500 HD and 3500 HD (2020–2025) are also covered. The bulletin is on NHTSA, but whether it is still current is not verified, so it is labelled vehicle data rather than confirmed.

  • 23-NA-073Status unverified

    P0442, P0446, P0455 or P0449 from dust plugging the EVAP canister and vent solenoid

    2019–2025silverado-1500, silverado-2500-hd, silverado-3500-hd · issued · NHTSA MC-11016945

    In very dusty use, dust can get into the canister and vent solenoid and set leak or vent codes. GM prescribes adding an inline filter between the canister and its fresh-air inlet, paid by the customer, and treats the filter as a maintenance item. The same bulletin covers GMC Sierra 1500 (2019–2025) and Sierra 2500 HD/3500 HD (2020–2025); cab-and-chassis (ZW9) trucks are excluded.

    We couldn't confirm whether this bulletin is still current, so it doesn't count as confirmation.

GMC

  • 2019–2025 · Sierra 1500

    Supported by vehicle data

    The same GM bulletin (23-NA-073) covers the Sierra 1500 and the 2020–2025 Sierra 2500 HD/3500 HD for P0446, P0449, P0442 and P0455 caused by dust in the canister and vent solenoid. The bulletin is on NHTSA, but whether it is still current is not verified, so it is labelled vehicle data rather than confirmed.

  • 23-NA-073Status unverified

    P0442, P0446, P0455 or P0449 from dust plugging the EVAP canister and vent solenoid

    2019–2025silverado-1500, silverado-2500-hd, silverado-3500-hd · issued · NHTSA MC-11016945

    In very dusty use, dust can get into the canister and vent solenoid and set leak or vent codes. GM prescribes adding an inline filter between the canister and its fresh-air inlet, paid by the customer, and treats the filter as a maintenance item. The same bulletin covers GMC Sierra 1500 (2019–2025) and Sierra 2500 HD/3500 HD (2020–2025); cab-and-chassis (ZW9) trucks are excluded.

    We couldn't confirm whether this bulletin is still current, so it doesn't count as confirmation.

  • P0449EVAP vent valve circuit fault

    Shares causes Supported by vehicle data

    P0449 is the electrical check on the same vent valve. GM links both to dust in the vent solenoid on some trucks.

  • P0455EVAP system large leak detected

    Shares causes Supported by vehicle data

    A vent that will not seal can fail the leak test, and GM lists P0446 and P0455 in the same dust bulletin.

  • P0442EVAP system small leak detected

    Shares causes Supported by vehicle data

    GM lists P0446 and P0442 in the same dust-intrusion bulletin.

All EVAP (evaporative emissions) codes

P0446 questions

Can topping off the tank cause P0446?

It can. Filling past the first click can push liquid fuel into the charcoal canister, which restricts the vent and can damage the valves. Stop at the first click.

I drive on dirt roads. Does that matter?

It can. GM has a bulletin for trucks where dust gets into the canister and vent solenoid in very dusty use, and the fix is an extra inline filter.

Is it safe to keep driving?

Usually yes, as long as there is no strong fuel smell and no fuel dripping. Most makers advise getting it fixed when it is convenient. A strong fuel smell means get it checked soon, and dripping fuel means stop and do not drive.

Will this code fail an emissions inspection?

In states that test OBD-II, a check engine light that stays on with the engine running fails the test. Clearing the code does not help straight away, because the EVAP monitor then reads not ready until the car completes a drive cycle.

Sources and review

  1. Frequently Asked Questions on On-Board Diagnostics (EPA 420-F-97-003) — US EPA ,
  2. On-Board Diagnostic II (OBD II) Systems Fact Sheet — California Air Resources Board ,
  3. EVAP: The Phantom Emissions Menace (Nissan TechNews, May 2018) — Nissan North America (hosted by AutomotiveTechInfo) ,
  4. OBD Test Reference (rev 8.6) — California Bureau of Automotive Repair ,
  5. What do you mean my car is not ready? — New York State DMV
  6. Recall acknowledgement 17V-088: BMW i3 REx fuel tank vent line may chafe — BMW of North America / NHTSA
  7. Part 573 Safety Recall Report 15V-621 (Mazda 8615J): liquid fuel can enter the EVAP canister — Mazda North American Operations / NHTSA
  8. GM 23-NA-073: P0442, P0446, P0455 or P0449 from dust intrusion into the canister and vent solenoid — General Motors / NHTSA ,
  9. Cal. Code Regs. Tit. 13, § 1968.2 — Malfunction and Diagnostic System Requirements (OBD II) — California Air Resources Board (via Cornell LII)
  10. Driveability Corner, August 2014 (Mark Warren) — MOTOR Magazine ,
  11. Toyota Camry Owner's Manual (OM06291U, 2.5L A25A-FKS / 3.5L 2GR-FKS) — Toyota
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Written by
Saurabh K.
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