Number P0446: EVAP System Vent Control Circuit
The evaporative emission (EVAP) system stores fuel vapour from the tank in a charcoal canister; a purge valve lets the engine draw it off, and a vent valve opens the canister to fresh air. The vent valve is normally open and closes for the leak test. By its wording P0446 is its control circuit, and
Can you drive with P0446?
Severity: Plan the repair. Yes — this is an emissions-system fault. The car will generally drive normally, but it will fail an emissions inspection with the light on.
If you ignore it: Fuel economy and emissions creep up, and some faults in this family (rich/lean running) stress the catalyst over time.
This is the #29 most common code in our top-150 library, in the evap — fuel vapor system family (Powertrain system). Severity is Number Nest's editorial triage — if the light is flashing or the car feels unsafe, stop driving it whatever any page says.
What P0446 means
The evaporative emission (EVAP) system stores fuel vapour from the tank in a charcoal canister; a purge valve lets the engine draw it off, and a vent valve opens the canister to fresh air. The vent valve is normally open and closes for the leak test. By its wording P0446 is its control circuit, and Ford uses it that way for open and shorted circuits. GM, however, uses P0446 for vent system performance – a blocked vent path: while purging with the vent valve open, the tank must not build up vacuum; more than 2989 Pa for 5 s before 4 litres have been purged sets the code, MIL after two trips. GM reports vent circuit faults as P0449, P0498 and P0499. A blocked vent makes refuelling difficult.
Systems involved: EVAP vent valve, vent filter, charcoal canister, engine control module (ECM/PCM).
Causes, ranked by likelihood
| # | Cause | Likelihood |
|---|---|---|
| 1 | Vent valve or filter blocked by dirt, dust or water (GM reading) | most likely |
| 2 | Vent valve electrically faulty, coil open or shorted (Ford reading) | possible |
| 3 | Connector or wire to the vent valve corroded or open | possible |
| 4 | Canister clogged with charcoal or liquid (overfilling) | possible |
| 5 | Vent hose kinked or blocked by an insect nest | less common |
Check them in order — the list is ranked so the likely, cheaper causes come before the expensive part.
Symptoms you may notice
- Check engine light on
- Refuelling problems, nozzle clicks off early (blocked vent)
- Hissing when opening the fuel cap (vacuum)
- EVAP leak test does not run
Misdiagnosis traps
- The vent valve lives under the car near the canister and inhales road dust and spider nests — a clogged vent filter mimics a dead valve.
- Overfilling the tank ("one more click") floods the canister with liquid fuel and sets vent and purge codes for weeks.
How a good shop confirms it
- Inspect the vent filter and hose for debris before condemning the solenoid; test the valve with power and vacuum.
Repair options & costs
| Repair | Shop total (parts + labor) | DIY (parts only) | Difficulty |
|---|---|---|---|
| EVAP purge valve / solenoid | $68 – $198 | $30 – $110 (parts only) | 1/5 |
National ranges from Number Nest's cost model (midsize car, independent shop, US-average labor). Published cross-check — EVAP purge valve / solenoid: CarMD 2026 national average $172.
OBDex repair data for this code rates the job difficulty medium with a typical labor time in the 0.5–2 hour range and DIY possible: yes.
Price this repair in your state
Estimated total: — (midsize car, independent shop)
Frequently asked questions
Why does the gas pump keep clicking off?
A venting fault is the classic cause: displaced air cannot escape the tank as fuel enters, so the nozzle senses a full tank. It is a symptom worth mentioning — it confirms the diagnosis.
How much does it cost to fix P0446?
The fix most associated with this code — evap purge valve / solenoid — runs $68 – $198 at an independent shop for a midsize car in our cost model (parts + labor, US average). The code names a system, not a part, so confirm the cause before spending: the ranked causes above are ordered by likelihood.
Can I drive with P0446?
See the can-you-drive verdict above — it is based on the system involved and the cascading-damage risk, and it is our editorial triage, not a manufacturer instruction. If the light is flashing or the car feels unsafe, stop driving it regardless of any code.
Will P0446 clear itself?
If the fault was a one-off (a loose cap, a cold-start glitch), the light can go out after several clean trips and the code ages into history. A fault that is still present re-sets the code as soon as the car runs that self-test again — monitors run under specific conditions, which is why "it hasn't come back in two days" is not proof of a fix.
Will my car fail inspection with P0446?
In states with OBD-based emissions inspection, yes — an illuminated check-engine light or an incomplete readiness monitor fails the test regardless of what the tailpipe would show. C-codes (ABS) fall under safety inspection instead in states that have one.
What should I check first for P0446?
The first item on the ranked-causes list above — it is ranked likelihood-first for exactly this reason — plus the free checks: recent work in the area (connectors left loose are a classic), fluid levels, and the battery and grounds on electrical codes.
Where this data comes from
Code facts, causes and symptoms come from OBDex — an open dataset of independently authored descriptions of the standardized generic OBD-II codes (CC0 1.0, public domain; github.com/foerbsnavi/OBDex). The SAE J2012 document itself is copyrighted and is not reproduced here. Cost ranges are Number Nest's own US planning model: national parts and labor ranges cross-checked against the CarMD Vehicle Health Index 2026 published averages, with labor adjustable by the BLS OEWS May 2025 state wage index for auto technicians (occupation 49-3023) — a wage index, not a surveyed shop rate. Severity and can-you-drive notes are our editorial triage, not a manufacturer instruction.