P0440: Evaporative emission (EVAP) system malfunction
The engine computer has found a fault in the fuel vapour (EVAP) system without the code naming the part: a leak, a valve or a sensor.
Updated
What P0440 means
Petrol gives off vapour. The EVAP system catches it in a charcoal canister, and a purge valve lets the engine draw it in and burn it. A vent valve lets fresh air into the canister and closes it off for the leak test, which a pressure sensor watches.
P0440 means the engine computer found a fault in the system without the code naming the part. The other codes on this page name it: the purge valve, the vent valve or the pressure sensor. The leak codes (P0442, P0455, P0456 and P0457) have their own page.
P0441 to P0454: purge valve, vent valve and pressure sensor
P0441 means the purge flow isn’t as expected, and P0443 to P0445 are faults in the purge valve’s circuit. P0446 to P0449 concern the vent valve and its circuit, and P0450 to P0454 the pressure sensor. The advice is the same for each; their own meaning and causes are shown below.
P0441: EVAP system incorrect purge flow
The flow of fuel vapour from the charcoal canister to the engine isn’t what the engine computer expects: too much or too little.
Common causes: purge valve stuck open, stuck closed or clogged, cracked, loose or blocked evap hose, faulty charcoal canister.
P0443: EVAP purge control valve circuit malfunction
The engine computer has found a fault in the electrical circuit of the EVAP purge valve, which lets fuel vapour from the charcoal canister into the engine to be burnt.
Common causes: faulty purge valve, wiring or connector fault, blown fuse.
P0444: EVAP System Purge Control Valve A Circuit Open
The engine computer has found a fault in the electrical circuit of the EVAP purge valve, which lets fuel vapour from the charcoal canister into the engine to be burnt.
Common causes: faulty purge valve, wiring or connector fault, blown fuse.
P0445: EVAP System Purge Control Valve A Circuit Shorted
The engine computer has found a fault in the electrical circuit of the EVAP purge valve, which lets fuel vapour from the charcoal canister into the engine to be burnt.
Common causes: faulty purge valve, wiring or connector fault, blown fuse.
P0446: EVAP vent control circuit malfunction
The engine computer has found a fault in the EVAP vent valve or its circuit. The vent valve lets air into the system and closes it for the leak test; one that stays closed can make refuelling difficult.
Common causes: faulty or stuck vent valve, wiring or connector fault.
P0447: EVAP System Vent Control Circuit Open
The engine computer has found a fault in the EVAP vent valve or its circuit. The vent valve lets air into the system and closes it for the leak test; one that stays closed can make refuelling difficult.
Common causes: faulty or stuck vent valve, wiring or connector fault.
P0448: EVAP System Vent Control Circuit Shorted
The engine computer has found a fault in the EVAP vent valve or its circuit. The vent valve lets air into the system and closes it for the leak test; one that stays closed can make refuelling difficult.
Common causes: faulty or stuck vent valve, wiring or connector fault.
P0449: EVAP vent valve/solenoid circuit malfunction
The engine computer has found a fault in the EVAP vent valve or its circuit. The vent valve lets air into the system and closes it for the leak test; one that stays closed can make refuelling difficult.
Common causes: faulty or stuck vent valve, wiring or connector fault.
P0450: EVAP System Pressure Sensor/Switch A Circuit
The signal from the EVAP pressure sensor, often called the fuel tank pressure sensor, is out of range or erratic, so the engine computer can’t run its leak test properly.
Common causes: faulty evap or fuel tank pressure sensor, wiring or connector fault, fuel cap or evap hose fault upsetting the reading.
P0451: EVAP pressure sensor range/performance
The signal from the EVAP pressure sensor, often called the fuel tank pressure sensor, is out of range or erratic, so the engine computer can’t run its leak test properly.
Common causes: faulty evap or fuel tank pressure sensor, wiring or connector fault, fuel cap or evap hose fault upsetting the reading.
P0452: EVAP System Pressure Sensor/Switch A Circuit Low
The signal from the EVAP pressure sensor, often called the fuel tank pressure sensor, is out of range or erratic, so the engine computer can’t run its leak test properly.
Common causes: faulty evap or fuel tank pressure sensor, wiring or connector fault, fuel cap or evap hose fault upsetting the reading.
P0453: EVAP System Pressure Sensor/Switch A Circuit High
The signal from the EVAP pressure sensor, often called the fuel tank pressure sensor, is out of range or erratic, so the engine computer can’t run its leak test properly.
Common causes: faulty evap or fuel tank pressure sensor, wiring or connector fault, fuel cap or evap hose fault upsetting the reading.
P0454: EVAP System Pressure Sensor/Switch A Circuit Intermittent
The signal from the EVAP pressure sensor, often called the fuel tank pressure sensor, is out of range or erratic, so the engine computer can’t run its leak test properly.
Common causes: faulty evap or fuel tank pressure sensor, wiring or connector fault, fuel cap or evap hose fault upsetting the reading.
Can I keep driving?
Check soon
Probably OK to drive short-term, but have it checked soon. If the engine is hard to start after refuelling, idles roughly or stalls, have it checked before driving far. If you smell fuel strongly or see fuel dripping, don’t drive: have it checked first.
General guidance based on the code alone, not on the car’s actual condition. If in doubt, stop and ask a mechanic.
Most of these faults don’t change how the car drives. The exception is a purge valve stuck open: it lets fuel vapour into the engine when it shouldn’t, which can make the engine hard to start after refuelling, idle roughly or stall. A vent valve that stays closed can make refuelling difficult.
Symptoms
- Usually only the check engine light.
- Hard starting just after refuelling, a rough idle or stalling, if the purge valve sticks open.
- Difficulty refuelling, if the vent valve stays closed.
- A smell of fuel near the car, on some cars.
Common causes
- Fuel cap not sealing. P0440 can also come from a leak. Check that the cap is closed properly and its seal is undamaged.
- Faulty purge or vent valve. Valves can stick open or closed, or fail electrically.
- Cracked or blocked EVAP hose, or a faulty charcoal canister. Hoses around the tank, the canister and the engine age and crack.
Typical fixes
- Check the fuel cap, and look over the EVAP hoses for cracks and loose ends.
- Check the plug and wiring of the part the code names: the purge valve, the vent valve or the pressure sensor.
- Have the valves tested for sticking and the sensor’s reading checked.
- Clear the code after the repair. The Evaporative system self-test under emissions readiness shows when the car has tested the system again, which can take several days of normal driving.
Questions
Can I drive with P0440?
Probably for a short time, but have it checked soon. If the engine is hard to start after refuelling, idles roughly or stalls, have it checked before driving far. If you smell fuel strongly or see fuel dripping, don’t drive: have it checked first.
Can a purge valve cause starting problems?
Yes. A purge valve stuck open lets fuel vapour into the engine when it shouldn’t, which can make it hard to start, especially just after refuelling, and give a rough idle.