fault code guide
P0446: EVAP Vent Control Circuit Malfunction
A valve controlling the release of fuel vapour from your charcoal filter has an electrical or flow fault. The car drives normally, but it releases more fumes and will fail emissions checks.
How it shows up: The amber engine management light will glow steadily on your dashboard, and the P0446 code can be retrieved with an OBD diagnostic scanner. You might also notice petrol pumps clicking off constantly when refuelling, or a faint petrol smell near the rear of the car.
Updated 9 November 2026
Can I keep driving?
Service soon
The car will run normally without damaging the engine, but unvented tank pressure can make refuelling difficult and will cause an MOT fail.
What to do right now
- 1Check your instrument cluster to confirm the engine management light is steady amber, not flashing.
- 2Make sure your fuel cap is properly closed and clicks shut securely.
- 3Note whether the fuel pump clicks off repeatedly during your next fill at the petrol station.
- 4Book an appointment with a local garage to have the vent circuit tested within the next week or two.
Likely causes
Most likely first.
- Likely
Faulty EVAP vent control solenoid
The vent valve mounted near the charcoal canister under the car gets exposed to road dirt, moisture and salt, causing its internal coil to fail or the valve to stick closed.
- Possible
Damaged or corroded wiring harness
Road debris or corrosion can break the wires or oxidise the connector pins leading to the vent solenoid, interrupting the electrical signal to the engine computer.
- Possible
Blocked charcoal canister or vent hose
Spider webs, road grime or degraded charcoal fragments can plug the vent tube, preventing air from flowing even when the electrical valve opens properly.
- Rare
Faulty fuel tank pressure sensor
The engine computer detects vent operation by monitoring tank pressure drops, so a failing sensor can falsely report a vent circuit malfunction.
What you can check yourself
Park somewhere safe and level, engine off, before you start.
- 1
Inspect the fuel cap
Turn off the engine, open the fuel flap and inspect the fuel cap seal for cracking or dirt. Tighten it until it clicks firmly, as an improper seal can upset evaporative pressure tests.
- 2
Check refuelling behaviour
The next time you fill up at a petrol station, see if the pump nozzle cuts out every few seconds. If the pump constantly clicks off, fuel tank air cannot escape, pointing directly to a shut vent valve.
- 3
Look under the rear for damaged wiring
With the car parked safely on level ground and the handbrake on, peer underneath near the fuel tank and spare wheel well. Look for dangling cables, torn insulation or loose plugs near the black plastic charcoal canister without crawling underneath.
Rough cost to fix
Rough estimateTypical prices in Ireland (€) and the UK (£), from an independent garage up to a main dealer. The total cost depends mainly on whether only the vent valve needs renewal or if dirt and saturation require replacing the entire charcoal canister assembly.
EVAP vent valve replacement
- Do it yourself
- €40–110£35–95 in the UK
- At a garage
- €140–260£120–220 in the UK
Vent solenoid wiring or connector repair
- Do it yourself
- €15–45£10–40 in the UK
- At a garage
- €100–190£85–160 in the UK
Charcoal vapour canister replacement
- Do it yourself
- Garage job
- At a garage
- €250–480£210–420 in the UK
When to go to a garage
- You smell raw petrol fumes inside the cabin or strongly around the vehicle.
- The engine management light begins flashing while driving.
- You are unable to put fuel into the tank because the pump nozzle cuts out immediately.
Questions drivers ask
Can I keep driving with code P0446?
Yes, you can drive normally for the short term because this fault relates strictly to fuel vapour containment rather than engine lubrication or cooling. However, leaving it unresolved can eventually saturate your charcoal canister or make filling your tank very frustrating.
Will P0446 cause an NCT or MOT failure?
An illuminated engine management light is an automatic fail on the UK MOT for petrol cars registered from July 2003 and diesels from July 2008. On the Irish NCT, an engine light or emissions code alone results in an Advisory Pass, failing only if exhaust emissions exceed legal thresholds or prevent test completion.
What is the difference between P0446 and P0455?
Code P0455 indicates a gross physical vapour leak somewhere in the system, often caused by a missing or loose fuel cap. In contrast, P0446 specifically points to an electrical or flow blockage problem with the canister vent control valve itself.
Can I simply clear the code to turn off the engine light?
Clearing the code will turn the dashboard light off temporarily, but the engine computer runs an evaporative self-test whenever your fuel level is between roughly one-quarter and three-quarters full. As soon as the test runs and detects the vent valve not responding, the light will illuminate again.
Test rules here are for the National Car Test in Ireland (NCT) and the MOT in the UK. Elsewhere, check the regulations of your own country or state before going for a vehicle test.
The warning light you may see
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General guidance for most cars, not a diagnosis of yours. Details differ by make, model and year - check your handbook, and if in doubt, don't drive.