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OBD fault code guide

P0446 Code Meaning UK

P0446 means “Evaporative Emission Control System Vent Control Circuit”. In plain English, the engine computer has detected a problem with the EVAP vent valve or the way the fuel vapour system vents and seals. Common causes include a faulty vent valve, blocked vent filter, damaged vent hose, charcoal canister restriction, wiring fault or EVAP pressure sensor issue.

📅 Updated June 2026 🇬🇧 UK diagnostic guide 🛠 EVAP vent control fault
Quick answer Fault codes hub EVAP system fault
✓ P0446 meaning ✓ Vent valve checks ✓ UK repair costs ✓ MOT-aware advice
Quick answer Meaning Symptoms Causes Diagnosis Vent checklist Repair costs Can you drive? MOT impact Related guides FAQs
Quick answer

What does P0446 mean?

P0446 means the ECU has detected a fault with the EVAP vent control system. The vent valve allows fresh air into the EVAP system and helps the system seal during self-tests. If the vent valve is stuck, blocked, electrically faulty or the vent path is restricted, the ECU may not be able to test the fuel vapour system properly.

Most likely area

Vent valve, vent filter, charcoal canister, vent hose, wiring, connector, ground or EVAP pressure sensor.

Urgency

Usually moderate if the car drives normally, but urgent if there is a strong petrol smell or visible fuel issue.

MOT risk

Can affect engine warning light status, emissions monitoring and fuel vapour safety.

Code meaning

P0446 — EVAP Vent Control Circuit

The full description is usually P0446 Evaporative Emission Control System Vent Control Circuit. This code points more towards the vent side of the EVAP system rather than a simple small leak.

The vent valve is usually fitted near the charcoal canister, often towards the rear or underside of the vehicle. It can be exposed to road dirt, water, salt and debris, which is why blocked vents and corroded connectors are common.

Mechanic view

Why P0446 is different from a normal EVAP leak

With P0442, I am thinking “small leak”. With P0455, I am thinking “large leak”. With P0446, I am thinking “can the EVAP system breathe and seal when commanded?”

A blocked vent path can make the system behave incorrectly even when there is no obvious broken pipe. That is why the vent valve, vent filter and charcoal canister need proper checks.

Symptoms

Common symptoms of a P0446 code

P0446 often causes no major driveability issue, but it can create fuelling, refuelling or vapour-control symptoms.

Engine management light

A steady engine warning light is the most common symptom.

Petrol smell

You may notice fuel vapour smell if the EVAP system is not venting correctly.

Difficulty refuelling

A blocked vent path can sometimes make the pump click off repeatedly while filling.

No obvious symptoms

Many cars drive normally with P0446 because the fault is in the vapour system.

Hard starting after fuel

EVAP valve problems can sometimes cause starting issues after refuelling.

EVAP readiness issue

The EVAP monitor may not complete until the vent fault is repaired.

Common causes

What causes a P0446 fault code?

P0446 is usually caused by a vent valve fault, vent restriction or electrical problem on the vent control side of the EVAP system.

Very common

Faulty EVAP vent valve

The vent valve may stick open, stick closed or fail electrically.

Restriction

Blocked vent filter

Dirt, dust, road debris or insects can block the vent filter or breather path.

Hose issue

Blocked or damaged vent hose

A kinked, crushed or split vent hose can stop the system venting properly.

Canister

Charcoal canister restriction

A damaged or saturated charcoal canister can restrict vapour flow.

Electrical

Vent valve wiring fault

Broken wires or corroded connectors can stop the valve being controlled.

Ground fault

Poor valve ground

A poor ground can prevent the valve from switching correctly.

Sensor

EVAP pressure sensor issue

Incorrect pressure readings can make the ECU think vent control has failed.

Fuel system

Fuel tank venting issue

A tank or filler venting restriction can affect EVAP self-tests and refuelling.

Previous repair

Disconnected vent line

Vent hoses can be disturbed during fuel tank, canister or underside repairs.

Diagnosis

How a garage should diagnose P0446

✅ Scan all stored, pending and permanent codes.

✅ Check whether P0440, P0442 or P0455 are also present.

✅ Inspect the vent valve location, usually near the charcoal canister.

✅ Check vent valve connector, wiring and ground.

✅ Command the vent valve open and closed with a scan tool where possible.

✅ Check whether the vent valve clicks and seals correctly.

✅ Inspect vent filters and hoses for blockage or damage.

✅ Smoke test the EVAP system if leaks are suspected.

✅ Check EVAP pressure sensor response during vent operation.

Avoid this mistake

Do not only change the fuel cap

A fuel cap can cause EVAP faults, but P0446 is more focused on vent control. If the cap is fine, the vent valve and vent path need checking.

Replacing a cap repeatedly will not fix a stuck vent valve, blocked vent filter or corroded connector near the charcoal canister.

EVAP vent control checklist

Mechanic-style checks for P0446

A good P0446 diagnosis checks whether the EVAP system can vent, seal and report pressure correctly.

Vent valve command

Use a scan tool to command the valve and confirm it reacts.

Vent path check

Check the vent filter and hose route for mud, debris or restriction.

Electrical test

Check power, ground and connector condition at the vent valve.

Pressure response

Watch tank pressure data while commanding the vent valve.

Canister inspection

Inspect for cracks, fuel saturation or restricted charcoal canister flow.

Refuelling clue

Repeated pump shut-off can point towards venting restriction.

UK repair cost guide

How much does P0446 cost to fix in the UK?

Costs vary by vehicle, vent valve location, corrosion, access and whether the fault is a valve, hose, wiring or canister restriction. These are rough UK guide prices only.

Diagnostic scan and valve test

Usually around £40–£120 depending on how much EVAP testing is included.

Vent valve replacement

Often moderate cost, but access near the tank or canister can affect labour.

Vent hose repair

Can be modest if the hose is easy to reach, but tank-area hoses can take longer.

Wiring or connector repair

Costs depend on corrosion, broken wiring and access underneath the vehicle.

Charcoal canister repair

Can cost more if the canister is damaged, saturated or hard to access.

Smoke or pressure testing

Useful if the system has both vent control faults and leak codes.

Safe driving advice

Can you drive with a P0446 code?

If the car runs normally, the engine light is steady and there is no strong petrol smell, short careful driving is usually possible. However, P0446 should still be repaired because it affects the fuel vapour control system and can stop emissions readiness checks from completing.

✅ Lower risk: steady engine light, no petrol smell, no visible leak and normal driving.

⚠️ Medium risk: difficult refuelling, repeat warning light or fuel vapour smell.

🚫 Higher risk: strong petrol smell, visible fuel leak, dripping fuel or fire-risk concern.

Real experience

What I would check first

On a real P0446 job, I would not stop at the fuel cap. I would look at the vent valve and charcoal canister area, because the vent side often lives underneath the vehicle where dirt and corrosion can cause problems.

If the customer says the fuel pump keeps clicking off while filling, that is a useful clue. It can point towards a venting restriction rather than a simple vapour leak.

MOT implications

Will P0446 fail an MOT?

P0446 can lead to an MOT failure if the vehicle has an emissions-related engine warning light, strong fuel smell, visible fuel leak, poor emissions or obvious fuel system safety concerns. EVAP faults are emissions-related, and fuel vapour issues should be treated seriously.

Engine warning light

An emissions-related engine light should be investigated before MOT.

Fuel vapour smell

A strong petrol smell can indicate a vapour or fuel system fault.

Fuel leak concern

Any visible fuel leak is a safety issue and must be repaired immediately.

Engine light MOT guide Common MOT failures
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Browse more OBD fault code guides

P0446 is one common EVAP vent control diagnostic trouble code. For more common codes, meanings, symptoms, repair costs and MOT implications, use the main Motor Vehicle Expert fault-code hub.

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Frequently asked questions

Frequently Asked Questions About P0446

Find answers to common questions about P0446 EVAP vent control faults, fuel vapour issues, driving safety, repair costs and MOT implications.

What does P0446 mean?

P0446 means the engine computer has detected a fault with the EVAP vent control circuit or vent control system. The vent valve helps the EVAP system seal and vent fuel vapours correctly.

Can I drive with a P0446 code?

You can usually drive carefully with P0446 if the car runs normally and there is no strong petrol smell. However, the fault should be repaired because it can affect emissions, fuel vapour control and EVAP readiness checks.

Will P0446 fail an MOT?

P0446 can lead to an MOT failure if it causes an emissions-related engine warning light, strong fuel smell, visible fuel leak, poor emissions or obvious fuel system safety concerns.

What causes a P0446 code?

Common causes include a faulty EVAP vent valve, blocked vent filter, damaged vent hose, charcoal canister restriction, wiring fault, corroded connector, poor valve ground, EVAP pressure sensor issue or blocked vent path.

How much does P0446 cost to fix in the UK?

A diagnostic check may cost around £40 to £120. Vent valve, hose or wiring repairs may be moderate, while charcoal canister or tank-area access repairs can cost more depending on the vehicle.

Is P0446 the same as P0440?

No. P0440 is a general EVAP system malfunction, while P0446 points more specifically to the EVAP vent control circuit or venting side of the EVAP system.

About this guide

Based on practical mechanic-style diagnostic experience

Motor Vehicle Expert publishes practical UK vehicle guidance based on real-world mechanical knowledge and hands-on diagnostic experience. This P0446 guide is written to help drivers understand EVAP vent control faults before replacing parts unnecessarily.

Fault codes should always be treated as a starting point for diagnosis. If your car has a strong petrol smell, visible fuel leak, difficult refuelling, rough running or a flashing engine light, get professional help.