Emissions control: EGR, DPF, catalytic converter and AdBlueGeneric OBD-II codeUrgency: Monitor
Code P0446: EVAP: vent valve circuit fault
P0446 means: evaporative emission control system (EVAP): vent control circuit.[1][2] The canister vent valve (or canister close valve) lets air into the EVAP system and is the one the control unit closes to run the leak test. P0446 indicates that the control unit cannot properly control the electrical circuit of that valve: it may be open (broken wire, corroded connector, dead coil) or short-circuited.[1][2]
What code P0446 means
The canister vent valve (or canister close valve) lets air into the EVAP system and is the one the control unit closes to run the leak test. P0446 indicates that the control unit cannot properly control the electrical circuit of that valve: it may be open (broken wire, corroded connector, dead coil) or short-circuited.[1][2]
It is a fault in the vent circuit, not a vapour leak: AutoDTCs points out that a car can have P0446 with the vapour system intact. Samarins describes it more broadly, as a fault or blockage in the vent part of the EVAP system, and warns that the description varies by manufacturer and that the code does not point directly to a part.[1][2]
While the code is active, the EVAP monitor does not complete and the control unit cannot run the leak test. Clearing the code is only a temporary measure, because it returns at the next full driving cycle.[1]
Original definition (SAE J2012): Evaporative Emission Control System Vent Control Circuit[1][2]
Causes of P0446
From most to least likely, according to the sources.
- 1Faulty vent solenoid valve, with an open or short-circuited coil.[1][2]
- 2Corroded valve connector, with water or protruding terminals. It is underneath the car, near the tank, and AutoDTCs warns that the fault is often in the connector before the valve.[1][2]
- 3Open wiring or high resistance between the control unit and the valve, due to salt, heat or chafing against the body; AutoDTCs also cites wires gnawed by rodents in the rear harness.[1][2]
- 4Blockage in the vent hose, the vent filter or the valve itself. Samarins mentions dust and insects nesting in the filter of a car that has been parked for a long time.[2]
- 5Other EVAP parts, according to Samarins: faulty canister, leak in the system, faulty tank pressure sensor, purge valve stuck open or, on Toyota and Lexus, the vacuum switching valve (VSV).[2]
- 6Output stage of the control unit: a rare cause that is only suspected once the wiring and valve are confirmed good.[1]
Symptoms
- Engine fault warning light on, often the only symptom.[1]Engine warning light: faults that cause it
- The EVAP monitor does not complete, so the car cannot finish the emissions test.[1]
- Slow tank filling or unusual pressure noises if the valve stays closed.[1]
- A slight smell of petrol vapour if the valve stays open.[1]Fuel smell: faults that cause it
How to diagnose P0446
In order: from the most likely and cheapest to check to the most expensive.
- 1Read all the codes. If there are other EVAP codes (P0440, P0441, P0455, P0456), AutoDTCs advises resolving P0446 first, because the valve must close for the leak test to run, and leak codes may disappear afterwards.[1]
- 2Inspect the vent valve and its two-wire connector: greenish corrosion, protruding terminals and water. Also check that the vent hose and vent filter are not blocked.[1][2]
- 3With the connector disconnected, measure the coil resistance. AutoDTCs gives a typical value of between 20 and 40 ohms and asks you to confirm the figure for the car: an open circuit indicates a broken coil, and an almost zero value a short circuit. Samarins notes that the valve is a solenoid that closes when voltage is applied, and that on Toyota the VSV is tested with 12 V: it should click.[1][2]
- 4If the resistance is correct, check the wiring: with a bidirectional tool commanding the valve, look for battery voltage on one terminal and a control unit–switched earth on the other, and check for voltage drop under current, which a resting measurement does not detect.[1]
- 5If you find nothing, carry out a smoke test of the system or an active EVAP test with diagnostic equipment. Samarins warns that not all workshops have the equipment and you may need to go to a larger one.[2]
- 6If the code returns after replacing the valve, suspect the wiring or the connector: they may look clean and still have enough resistance to fail the circuit test.[1]
Can I keep driving with P0446?
Monitor
AutoDTCs rates it as low severity: P0446 rarely affects driving or fuel consumption, because the valve only works during the leak test, but it prevents the EVAP monitor from completing and guarantees that an emissions inspection will be failed while the code is active. The car can be driven, and it is worth repairing to pass the inspection and to turn off the light.[1]
Documented faults related to P0446
Known faults of specific engines and cars, with their repair cost, the affected years and their sources.
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.
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.
Frequently asked questions
Can I drive with code P0446?
Yes. It is an electrical fault in the EVAP vent circuit and does not affect the engine. The car will not pass an emissions inspection while the code is active, and the light will stay on until it is repaired.[1]
Does it mean there is a petrol leak?
No. AutoDTCs explains that it is a fault in the vent valve circuit and not a hole in the vapour path, and that the leak codes (P0440, P0455, P0456) are separate. It can appear with the vapour system intact.[1]
What is the difference between P0446 and P0449?
Both relate to the canister vent valve circuit. P0449 is set when the electrical response of the valve or its solenoid is not as expected; P0446 is the more general warning for the vent control circuit, whose definition varies by manufacturer. Diagnosis of both starts in the same place: valve, connector and wiring.[1][2]
Does clearing the code fix it?
Only temporarily. AutoDTCs explains that the code returns at the next full driving cycle if the fault is still there, because the EVAP monitor cannot complete.[1]
Will I pass the MOT with code P0446?
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.[3]
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.
- P0446: Evaporative Emission System Vent Control CircuitAutoDTCs · Technical documentation · consulted 31 October 2026
- P0446 Evaporative Emission Control System Vent Control Circuit MalfunctionSamarins.com · 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