Emissions control: EGR, DPF, catalytic converter and AdBlueGeneric OBD-II codeUrgency: Monitor
Code P0440: EVAP system: malfunction
P0440 means: evaporative emission control system (EVAP): malfunction.[1][2][3] The EVAP system captures petrol vapours from the tank in an activated carbon filter (canister) and sends them to the intake to be burned when the engine is in the right conditions. P0440 is the most generic warning from that system: the control unit has detected that something is not working as it should, but the code does not confirm a leak or point to the faulty part.[1][2]
What code P0440 means
The EVAP system captures petrol vapours from the tank in an activated carbon filter (canister) and sends them to the intake to be burned when the engine is in the right conditions. P0440 is the most generic warning from that system: the control unit has detected that something is not working as it should, but the code does not confirm a leak or point to the faulty part.[1][2]
To check this, the control unit commands the vent valve and the purge valve to specific positions and measures the resulting pressure or vacuum. AutoDTCs explains that the code is stored when the system does not respond within the expected range in that self-test, and that the cause can be a component that prevents the test from being done correctly, a wiring fault or an intermittent condition that interrupts it. Mechanic Base adds that the exact detection conditions vary by brand and model.[1][2]
Unlike P0442 and P0455 (small leak and large leak), P0440 does not indicate the size of any leak. On Volkswagen Group cars, Ross-Tech associates it with a leak in the system or a fault in the purge regulator valve (N80) or the purge solenoid valve (N115).[2][3]
Original definition (SAE J2012): Evaporative Emission Control System Malfunction[1][2][3]
Causes of P0440
From most to least likely, according to the sources.
- 1Fuel cap loose, damaged or not the correct one, or a damaged seal on cars with a capless filler. Mechanic Base lists it first, and AutoDTCs describes it as the first thing to check for any EVAP code.[1][2]
- 2Cracked, disconnected or blocked EVAP hose or pipe.[1][3]
- 3Faulty purge valve or vent valve: stuck, or with a damaged coil or connector. AutoDTCs cites a vent valve that does not close fully and a stuck purge solenoid valve.[1][2][3]
- 4Damaged, cracked or saturated activated carbon filter (canister).[1][2]
- 5Faulty fuel tank pressure sensor or another sensor in the system.[1][2]
- 6Damaged wiring or a loose, corroded or deteriorated connector on the purge valve or the vent valve.[1][2]
- 7Leak or fault in the tank or the filler neck.[1]
Symptoms
- Engine fault warning light on; it may be the only symptom.[1][2][3]Engine warning light: faults that cause it
- A slight smell of petrol near the car, especially by the filler neck.[1][2]Fuel smell: faults that cause it
- The fuel nozzle clicks off several times or it is difficult to fill the tank.[1]
- The EVAP readiness test is incomplete or not ready, and the car would not pass an emissions inspection that reads the OBD system.[2]
How to diagnose P0440
In order: from the most likely and cheapest to check to the most expensive.
- 1Read the stored and pending codes and note the freeze frame data before clearing anything. If there are other EVAP codes (P0442, P0446, P0455…), repair those first. Mechanic Base warns that a basic reader may not be enough to diagnose the EVAP.[1][2]
- 2Check the cap: that it closes properly and the seal is not damaged. On cars with a capless filler, clean and check the filler neck seal. Then clear the code and complete a driving cycle so the EVAP monitor runs again.[1][2]
- 3With the engine off and cold, inspect the EVAP hoses and connectors: disconnections, cracks, pinches and loose connectors.[1][2]
- 4With a bidirectional diagnostic tool, command the vent valve to close and the purge valve to open, listen for clicks and watch how the tank pressure sensor responds. With the valve disconnected, AutoDTCs gives a typical coil resistance of about 20 to 40 ohms; confirm the exact figure in the car's manual.[1][2][3]
- 5If you see nothing, carry out a smoke test of the circuit at the pressure stated in the manual. Mechanic Base warns against using workshop compressed air or improvised pressures.[1][2]
- 6Do not replace the purge valve or the canister without testing first: Mechanic Base warns that replacing parts blindly may mean spending money without fixing anything.[1]
- 7After repair, check that the EVAP monitor completes without the code returning. AutoDTCs recommends starting from cold if possible, with the tank between 15 and 85% and about 15 to 20 minutes of mixed city and road driving. Clearing the codes resets the readiness monitors.[1][2]
Can I keep driving with P0440?
Monitor
AutoDTCs rates it as low severity, with no effect on driving or safety, and advises repairing it before an emissions inspection. Mechanic Base accepts short journeys to reach the workshop if the light is steady and the engine runs normally, but asks you to stop and check if there is liquid fuel, a strong smell of petrol, stalling or difficulty starting, and warns that a flashing light can indicate another engine problem that needs immediate attention.[1][2]
Documented faults related to P0440
Known faults of specific engines and cars, with their repair cost, the affected years and their sources.
Engine sensors: the most serious faults by engine and car
- High severityFrequency: Occasional2.0 DTI and 2.2 DTIVP44 injection pump and air mass meter failureGerman Wikipedia documents recurring failures of the Bosch VP44 injection pump and the air mass meter in the early years of this engine. An owner testimony for this engine describes the pump being replaced at 192,500 km, at a cost the owner calls «prohibitive».
- Medium severityFrequency: Common2.0 TDIClogged particulate filter or faulty pressure sensorThe 2.0 TDI's particulate filter clogs if the car mostly makes short journeys, because it never gets to regenerate; sometimes the fault is just the differential pressure sensor. Cleaning it costs around €200 and replacing it, €800 to €3,000.Repair (garage): €800–€3,000
- Medium severityFrequency: Common1.4 and 1.6 8vCrankshaft position sensor failure (TDC sensor)The crankshaft position sensor (capteur PMH, or TDC sensor) appears repeatedly in the reliability sources for the Clio II, the Kangoo I and the Dacia Logan I with this engine, with hard cold starting or stalling as the main symptoms. It is a cheap part, but the failure can leave you stranded.
- Medium severityFrequency: Common1.4 and 1.6 16vCrankshaft position sensor failureThe crankshaft position sensor (capteur PMH) appears repeatedly in the reliability sources for almost every generation with this engine, with hard cold starting, stalling or the car cutting out unexpectedly. It is a cheap part, but the failure can leave you stranded.
Wiring, connectors and short circuits: the most serious faults by engine and car
- Critical severityFrequency: OccasionalBMW N62 / N63Additional turbo coolant pump with a risk of short circuit and fireIn 2011 BMW recalled 5, 6 and 7 Series, X5 and X6 models built between 2007 and 2011 because of the additional turbo coolant pump: moisture, a short circuit and, in extreme cases, a fire. In 2012 there was another campaign for a crack in the pump, with a more robust version.
- Critical severityFrequency: Occasional1.6 GDi híbrido (Kappa)Main relay of the power relay assembly (overheating and fire risk)Yes, on the first units: Hyundai and Kia recalled 2016–2018 Ioniq and Niro hybrids and plug-in hybrids because the main relay that connects the high-voltage battery could come loose, overheat and, in the worst case, cause a fire.
- Critical severityFrequency: Occasional1.6 GDi híbrido (Kappa)Clutch hydraulic actuator (HCA): leak or moisture with risk of short circuit and fireYes, this is the most documented hybrid system fault: the hydraulic actuator that engages the combustion engine with the hybrid assembly has had two recalls (2018 for a leak on the Niro and 2025 for moisture in its electronic board on the Niro, Ceed and XCeed PHEV), with a risk of short circuit and fire.
- High severityFrequency: Occasional1.3 TCeBlown fuel pump fuseOn the Renault Captur II and Clio V with the 1.3 TCe engine, a 20-amp fuse can blow and leave the car without an engine. According to L'argus, in April 2021 this fault still had no factory fix; the official service centre's diagnosis includes checking, and sometimes replacing, the catalytic converter.
- Critical severityFrequency: CommonRover 75Seat SRS connector fault with airbag and seatbelt warning light onAuto Express warns that the Rover 75's seat SRS connector can cause the airbags to fail, and dealers were fixing it with revised connectors. The Dutch APK inspection puts the airbag or seatbelt fault warning among the most frequent defects across almost all series.
- Critical severityFrequency: OccasionalAlfa Romeo GiuliettaShort circuit from badly routed wiring that can prevent gear shifting (KBA campaign, 2010-2015)Yes: according to Germany's KBA, on Alfa Romeo Giulietta cars built between 2010 and 2015 inadequate cable routing could cause a short circuit and, as a result, gear-shift failure.
Frequently asked questions
What is the difference between P0440 and P0442, P0455 and P0456?
P0440 indicates a general fault in the EVAP system without specifying its nature. P0442, P0455 and P0456 are leaks of different sizes (small, large and very small). AutoDTCs notes that P0440 does not specify the leak size as the other two do, and that it can appear without any physical leak.[1][2]
Can I drive with code P0440?
With the light steady and the car running normally, the sources consider it an emissions fault with no mechanical risk: you can drive it, but it is worth fixing before an emissions inspection. If there is a strong smell of petrol, liquid fuel, stalling or starting problems, stop and check the car.[1][2]
Is it always the fuel cap?
Not always, but it is the first thing to check because it is the cheapest. If tightening or replacing the cap and completing a driving cycle does not solve it, go on to the valves, hoses, canister, pressure sensor and wiring.[1][2]
The light has gone off; is it fixed?
Not necessarily. Mechanic Base explains that the light can go off after several self-tests without the problem being resolved, and that the code can remain stored. What confirms the repair is that the EVAP monitor completes without the fault reappearing.[1]
Will I pass the MOT with code P0440?
If the code has switched on the engine warning light, no: with that light on, the inspection records a serious defect, and on Euro 5 and Euro 6 cars the ITV (Spain's roadworthiness inspection, similar to the MOT) also reads the OBD diagnostic system. Repair the fault before you go; clearing the code just before the inspection does not help either, because it counts as a serious defect.[4]
Not sure what is wrong with your car? Describe what you notice in the symptom diagnosis or see all fault codes.
Sources
Every fact on this page links to its source. If you find an error, let us know.
- P0440 – Evaporative Emission Control System MalfunctionMechanic Base · Technical documentation · consulted 31 October 2026
- P0440: Evaporative Emission SystemAutoDTCs · Technical documentation · consulted 31 October 2026
- 16824/P0440/001088 - EVAP Emission Control Sys: MalfunctionRoss-Tech Wiki · Technical documentation · consulted 31 October 2026
- Desmontando mitos: ¿puede pasar mi coche la ITV con el testigo de «avería motor» encendido?Diariomotor · Motoring press · published 8 March 2021 · consulted 2 October 2026 · in Spanish