P0446
- Powertrain
- Generic (SAE)
- Emissions
Diagnose soon
Mostly an emissions and inspection issue with no safety risk, and it will block the EVAP monitor from completing. It rates above the lowest band because a vent stuck closed prevents the tank from breathing, which can make the fuel pump nozzle click off repeatedly during refuelling and, in the worst case, pull enough vacuum in the tank to affect fuel delivery.
- Safe to drive
- Safe to drive. If the filler neck hisses hard or the pump keeps clicking off, get it checked sooner.
Evaporative Emission Vent Control Circuit Malfunction
The computer found a problem with the vent valve circuit in the fuel vapour system. That valve seals the charcoal canister off from outside air so the system can be leak-tested. Depending on the manufacturer, this code covers either an electrical fault in the circuit or a valve that is not doing its job mechanically.
The vent valve sits between the charcoal canister and atmosphere. It is open during normal operation so the tank can breathe and the canister can be purged, and the module commands it closed to seal the system for a leak test. P0446 is set from the vent control circuit. The exact criteria vary meaningfully by manufacturer: some set it purely for an electrical open or short on the solenoid driver, while others also set it for a performance failure — the valve commanded closed but the fuel tank pressure sensor showing no vacuum developing, or a blocked vent path producing vacuum when none should exist. Always confirm which definition applies to the vehicle in front of you.
How the car detected itFor the electrical definition, the module watches feedback voltage on the solenoid control line with the driver both on and off, and flags an open circuit, a short to ground, or a short to voltage. For the performance definition, the module commands the vent closed, applies vacuum through the purge valve, and watches the fuel tank pressure sensor. No vacuum change implies the vent is stuck open or the circuit is dead; vacuum appearing with the vent commanded open implies the vent path is blocked or the valve is stuck closed.
A trouble code records what a control module measured. It does not identify which part failed. Test before replacing anything.
- Safe to drive
- Safe to drive. If the filler neck hisses hard or the pump keeps clicking off, get it checked sooner.
- Urgency
- Diagnose soon
- Will it pass emissions
- No
- If ignored
- The light stays on, the EVAP monitor never completes, and the vehicle fails emissions inspection. Any additional EVAP leak codes stored alongside cannot be trusted or properly diagnosed until the vent valve works, because the leak test depends on it sealing. If the valve is stuck closed rather than stuck open, expect increasingly awkward refuelling and, over time, possible fuel starvation symptoms as the tank cannot equalise pressure.
- Check engine light
- Solid
- Clearing the light
- A completed drive cycle is normally required before the monitor re-runs and the light can clear.
- Possible smell of fuel near tank or engine bay
- Failed emissions inspection
- Loose-cap warning may appear
Many vehicles show no symptom at all beyond the warning light. The absence of a symptom does not mean the fault is not real.
These are the causes this code can have. For the order to work through them in, see what to check first.
| # | Cause | How often | Component |
|---|---|---|---|
| 1 | Vent valve seized or contaminated by water/dirt | Very common | — |
| 2 | Wiring or connector fault | Common | — |
Ordering reflects how often each cause is responsible in general, not a probability for your vehicle. Confirm by testing.
In order. Each of these is cheaper or faster than what follows it, and each one can make the rest unnecessary.
Whether EVAP leak codes are stored alongside it
A vent valve that will not seal makes the leak test fail, so codes like P0455 or P0456 often appear with it. Fix the vent circuit first, then re-test — the leak codes may have no independent cause.
The vent valve connector
The vent valve is mounted low, usually near the canister at the rear, and takes constant road spray and salt. Corroded terminals and a water-filled connector body are the single most common cause of this code.
The vent inlet and its filter
Mud, snow pack, insect nests, and rodent nesting material block the vent path. On makes that use the performance definition, a blocked vent reads exactly like a failed valve and costs nothing to check.
Recent underbody damage or work
The vent valve, its harness, and the canister all sit in the impact zone for road debris and get disturbed during exhaust, tank, or suspension work.
Confirm what P0446 means on this specific vehicle
Tools Manufacturer service information
Pull the manufacturer's setting criteria before testing. An electrical-only definition and a performance definition lead to different tests, and guessing wrong wastes the whole diagnosis.
ExpectedClear statement of the failure criteria and the monitor's enabling conditions
Inspect the vent valve, connector, and vent path
Tools Light, hand tools, pick set
Locate the vent valve — position varies by vehicle, commonly near the charcoal canister at the rear. Separate the connector and look for green corrosion, water, or spread terminals. Check the vent inlet and filter for blockage.
ExpectedClean dry terminals, clear vent path
Command the valve with a bidirectional scan tool
Tools Bidirectional scan tool
Cycle the vent valve open and closed while listening and feeling at the valve body. A working solenoid clicks audibly. No click means no current reaching the coil, or a dead coil, or a seized valve.
ExpectedDistinct click on each command
Measure solenoid coil resistance
Tools Multimeter
Unplug the valve and measure across its terminals. An open reading confirms a failed coil. Typical values sit in the tens of ohms but the exact spec is vehicle-specific — compare against service data, not a generic figure.
ExpectedStable resistance within the manufacturer's stated range
Test supply and control circuits at the connector
Tools Multimeter, test light, wiring diagram
Key on, check for supply voltage at the feed terminal. Then check the control terminal for the module driver switching when the valve is commanded. If supply is missing, work back toward the fuse and the module.
ExpectedSupply near battery voltage; control line switching on command
Flow test the valve mechanically
Tools Low-pressure air source or smoke machine, scan tool
With the valve out or accessible, command it closed and apply gentle low pressure to the vent port — it should hold. Command it open and it should flow freely. This separates an electrically healthy valve that is mechanically seized from a genuine circuit fault.
ExpectedSeals fully when closed, flows freely when open
Voltage drop the supply and ground under load
Tools Multimeter
With the solenoid energised, measure the drop across the feed and the ground path. Corrosion in an underbody circuit passes a continuity check but collapses under load.
ExpectedUnder 0.5 V on each side
Re-run the EVAP monitor and verify
Tools Scan tool with readiness display
Clear codes after repair, then drive under conditions that let the EVAP monitor run — partly filled tank, moderate ambient temperature, several complete cold-to-warm cycles. Confirm the monitor sets complete and no leak codes follow.
ExpectedEVAP monitor complete, no returning codes
| Repair | Only after you confirm | Typical cost | Who |
|---|---|---|---|
| Replace the EVAP vent valve solenoid | Open or out-of-spec coil resistance, or a valve that will not seal when commanded closed, with supply and control circuits verified good | $110–$380 | DIY |
| Repair or replace the vent valve connector and harness section | Corroded or wet terminals, excessive voltage drop, or a control signal that appears only when the harness is flexed | $100–$350 | DIY |
| Clean or replace the vent filter and clear the vent inlet | Visible blockage plus restored flow through the vent path after clearing | $40–$220 | DIY |
| Replace the charcoal canister where the vent valve is integrated into it | Failed vent valve on a design where the valve is not separately serviceable | $280–$900 | Hard |
| Repair the module driver circuit or replace the module | Good valve and good wiring with no driver activity at the module output — verify twice before going here, it is rare | $400–$1,500 | Shop |
The solenoid itself is usually modest, but on some designs it is integrated into the canister assembly and cannot be bought separately, which multiplies the cost. Rust in the underbody fasteners is the other cost variable — seized canister bolts on an older vehicle can add substantial labour.
- Replacing the valve when the connector or harness is corroded. The valve lives in the harshest spot on the vehicle and the wiring usually fails before the solenoid does.
- Treating P0446 as a fuel cap problem. This is a circuit and valve code — tightening the cap does nothing for it.
- Ignoring the vent filter and inlet path. On performance-based strategies a blocked inlet produces this code with a perfectly good valve.
- Testing the solenoid warm, dry, and off the vehicle, where an intermittent open caused by moisture and vibration will not appear.
- Chasing accompanying leak codes first. With the vent valve unable to seal, the leak test result is meaningless — fix the vent circuit, then re-test.
- EVAP Vent Valve
- EVAP Vent Valve Wiring
- Definition
- Generic code set (SAE J2012 / ISO 15031-6) via the OBDexopen database, dedicated to the public domain under CC0-1.0.
- Diagnostic guidance
- Written and reviewed in-house. See our editorial policy.
- Review status
- Reviewed
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