Why won't my car take fuel — the pump keeps clicking off?

A blocked or stuck vent in the evaporative system is a common cause and often accompanies this code. As fuel goes in, the air and vapour it displaces has to escape through the charcoal canister's vent. If that path is restricted, pressure builds in the filler neck, fuel backs up and the pump nozzle's automatic cut-off trips repeatedly. It is not a fault with the pump at the station, and filling in small bursts is a workaround rather than a fix.

Will P0446 fail an MOT?

Yes, on the lamp, which is a major defect for petrol cars first used on or after 1 July 2003. There is an additional consequence specific to this code: the vent valve is what seals the system so the car can test itself, so with it faulty the evaporative readiness monitor cannot complete. If codes have been cleared before the test, that monitor will never come ready, and on many cars the emissions check cannot be completed until the monitors have run — which is a second, separate major failure.

Where is the EVAP vent valve located?

On most cars it is mounted underneath, at or very near the charcoal canister, which usually sits near the fuel tank towards the rear. That position is the reason it fails: it is directly exposed to road spray, salt and grit, so the valve body and its electrical connector corrode far more readily than components in the engine bay. Access is generally straightforward once the car is raised, though seized fixings are common on older cars.

Should I fix P0446 before other EVAP codes?

Yes. The vent valve is what allows the control unit to seal the fuel system and test it, so if it is not working the leak tests are unreliable and can report leaks that do not exist. Repairing the vent fault first and then rechecking often makes accompanying leak codes disappear on their own, whereas chasing those first risks replacing perfectly good hoses, valves and seals in pursuit of a leak the car only thought it saw.

Powertrain code · standard

P0446Fault in the fuel vapour system's vent valve or its circuit

Standard definition: Evaporative Emission Vent Control Circuit Malfunction

Last updated 27 July 2026

Quick answer

The vent valve lets the charcoal canister breathe fresh air, and closes to seal the fuel system whenever the car wants to test itself for leaks. The control unit has found it faulty electrically, or found it not opening and closing as it should. It lives under the car, so corrosion is the usual reason.

How the car works this out

The vent valve sits at the fresh-air end of the charcoal canister and is normally open, letting the canister draw and release air as the tank breathes and as vapour is purged into the engine. To run a leak test the control unit closes it, sealing the system so pressure or vacuum can be applied. The code is set either when the electrical circuit to the valve reads as open, shorted or drawing the wrong current, or when the valve's behaviour during a test does not match what closing and opening it should have produced.

What you might notice

Usually nothing while driving
The fuel pump nozzle repeatedly cutting out while refuelling, so the tank takes several attempts to fill
A petrol smell around the rear of the car
Other evaporative codes appearing alongside it, since the leak tests depend on this valve working

What causes it

Most likely first. A code names the check that failed, not the part that failed it, so more than one of these can produce the same number.

1Corrosion of the valve itself, which is mounted underneath the car near the canister and takes the full force of road salt and sprayCommon
How to check: Get the car up and look at it. A valve with a corroded body or a green, crusted connector is condemned on sight in this climate.
2A corroded or water-filled electrical connector at the valveCommon
How to check: Unplug and inspect the pins. Wiggling the connector while the valve is commanded on a diagnostic tool will show up an intermittent contact.
3A blocked vent line or vent filter, often from mud, debris or a crushed pipePossible
How to check: If the tank is also hard to fill, a restricted vent is a strong candidate, because the air displaced by incoming fuel has nowhere to go.
4A failed solenoid coil inside the valve, so it no longer moves at allPossible
5Chafed or broken wiring along the underbody run to the valvePossible
6Physical damage to the canister or valve from a kerb, a speed bump or a rear impactLess common

What to do about it

1Have the car put up and the valve looked at directly. Everything about this fault is underneath, exposed and visible, which makes it one of the more straightforward evaporative diagnoses.
2Check the connector as carefully as the valve. Water ingress into the plug is at least as common as the valve failing, and it is a far cheaper fix.
3If the tank has become difficult to fill, mention that when you book it in. Nozzle cut-out is a strong pointer at a vent restriction and saves the garage some hunting.
4Deal with this one before chasing any other evaporative codes. Every leak test the car runs depends on this valve sealing the system, so a vent fault can generate leak codes that are not real.
5Use a proper replacement valve. This part sits in the worst environment on the car and a poor-quality one will not last a winter.

Can you keep driving?

Yes

There is no safety or mechanical consequence, and the car will drive exactly as it always has. The practical irritation is refuelling: if the vent is restricted, the pump nozzle will keep clicking off and filling the tank becomes a slow business. Otherwise the fault sits there costing you nothing except the lamp.

Will it fail an MOT?

The lamp is the direct failure, as ever, and there is no evaporative measurement in the MOT to argue against it. What makes this code worth understanding at test time is its second-order effect. The vent valve is what makes the leak test possible at all, so with it faulty the evaporative readiness monitor generally cannot complete. That matters if anybody has cleared codes before the test, because the monitor will sit permanently incomplete rather than eventually running, and on many cars the emissions check cannot be finished until the monitors have — so the car fails on an incomplete emissions test as well as the lamp. Fixing the vent valve is a prerequisite for the car being able to prove anything about itself.

The light this turns on

Engine management lightThe engine management system has found a fault it cannot correct and has stored a code for it. The car will usually still drive, but an illuminated engine light is an automatic MOT failure on petrol cars first used from 1 July 2003 and diesels from 1 July 2008.

Common questions

Why won't my car take fuel — the pump keeps clicking off?: A blocked or stuck vent in the evaporative system is a common cause and often accompanies this code. As fuel goes in, the air and vapour it displaces has to escape through the charcoal canister's vent. If that path is restricted, pressure builds in the filler neck, fuel backs up and the pump nozzle's automatic cut-off trips repeatedly. It is not a fault with the pump at the station, and filling in small bursts is a workaround rather than a fix.
Will P0446 fail an MOT?: Yes, on the lamp, which is a major defect for petrol cars first used on or after 1 July 2003. There is an additional consequence specific to this code: the vent valve is what seals the system so the car can test itself, so with it faulty the evaporative readiness monitor cannot complete. If codes have been cleared before the test, that monitor will never come ready, and on many cars the emissions check cannot be completed until the monitors have run — which is a second, separate major failure.
Where is the EVAP vent valve located?: On most cars it is mounted underneath, at or very near the charcoal canister, which usually sits near the fuel tank towards the rear. That position is the reason it fails: it is directly exposed to road spray, salt and grit, so the valve body and its electrical connector corrode far more readily than components in the engine bay. Access is generally straightforward once the car is raised, though seized fixings are common on older cars.
Should I fix P0446 before other EVAP codes?: Yes. The vent valve is what allows the control unit to seal the fuel system and test it, so if it is not working the leak tests are unreliable and can report leaks that do not exist. Repairing the vent fault first and then rechecking often makes accompanying leak codes disappear on their own, whereas chasing those first risks replacing perfectly good hoses, valves and seals in pursuit of a leak the car only thought it saw.

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