Emissions control: EGR, DPF, catalytic converter and AdBlueGeneric OBD-II codeUrgency: Monitor
Code P0456: EVAP system: very small leak detected
P0456 means: evaporative emission control system (EVAP): very small leak detected.[1][2] The control unit has detected a very small leak in the EVAP system, the closed circuit that collects petrol vapours from the tank into the canister and sends them to the intake to be burned. It is the most subtle of the leak codes: what distinguishes it from P0442 and P0455 is the size of the leak, not the system.[1][2][3]
What code P0456 means
The control unit has detected a very small leak in the EVAP system, the closed circuit that collects petrol vapours from the tank into the canister and sends them to the intake to be burned. It is the most subtle of the leak codes: what distinguishes it from P0442 and P0455 is the size of the leak, not the system.[1][2][3]
AutoDTCs describes, for one specific Toyota system, a test with the engine off after several hours of rest: the leak detection pump in the canister module creates a slight vacuum, and the control unit compares the stabilised pressure with what corresponds to a calibrated 0.02-inch orifice. The test can last up to 20 minutes, and the light comes on after two failed cycles. This is the example for a single model, and other manufacturers use other conditions.[1]
In the Volkswagen Group, Ross-Tech defines it as “very small leak detected” and gathers notes on North American VW and Audi models with bulletins that foresee updating the control unit software or replacing the system's pressure sensor for natural vacuum leak detection (NVLD). Those notes do not state whether they affect units sold in Europe.[2]
It usually appears together with P0455 (large leak), according to Samarins.[3]
Original definition (SAE J2012): Evaporative Emission Control System Leak Detected (Very Small Leak)[1][2]
Causes of P0456
From most to least likely, according to the sources.
- 1Fuel cap seal damaged or cap not closed properly: the most common cause.[1][2]
- 2Vapour hose cracked or aged between the tank and the canister.[1]
- 3Filler neck seal or tank ventilation line connection to the canister faulty.[1]
- 4Cracked canister housing.[1]
- 5Vent valve seat of the pump module that does not close fully.[1]
- 6Purge valve mounting seal or gasket with a small leak when closed.[1]
Symptoms
- Engine fault warning light on, often after two failed test cycles.[1][2]Engine warning light: faults that cause it
- The EVAP monitor shows as incomplete or failed, with a risk of failing an emissions test.[1]
- A slight smell of petrol in the engine bay or near the filler neck, especially in the heat.[1]Fuel smell: faults that cause it
- No driving symptoms.[1]
How to diagnose P0456
In order: from the most likely and cheapest to check to the most expensive.
- 1Check the cap seal (cracks, crushing, dirt) and clean the sealing surface of the filler neck. Refit the cap until it clicks, clear the code and drive two full cycles with the engine warm. If it does not return, it was the cap. A cap tester can detect a faulty cap that looks sound.[1][2]
- 2Carry out a smoke test by connecting the machine to the EVAP service port, with the vent blocked and a pressure of about 0.5 psi. Very small leaks can take several minutes to show smoke. Common locations are the filler neck, the tank-to-canister hose and the purge valve seal.[1]
- 3Before blaming the monitor, check the tank level: above 90% the test may be invalid. With the tank between 50 and 80%, the car warm and parked for at least 5 hours, let the monitor run again before deciding the code persists.[1]
- 4Trace the hose connections from the tank to the canister and from the canister to the purge valve: disconnections, kinks, cracks in the elbows and poor seating on the spigots.[1]
- 5If there is no clear cause, look for technical bulletins for your model: Ross-Tech gathers several for VW and Audi.[2]
Can I keep driving with P0456?
Monitor
AutoDTCs rates it as low severity, with no risk to driving or safety. The car can be driven, but it would fail an emissions inspection, so it is worth repairing before that or within the next service interval.[1]
Documented faults related to P0456
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.
Frequently asked questions
Can I drive with code P0456?
Yes. AutoDTCs describes it as a leak so small that it does not affect driving or safety. The car would not pass an emissions inspection with the code active, so it is worth fixing before then.[1]
Why does the light take so long to go off after a repair?
Because the monitor only runs after sufficient rest and cannot be forced. AutoDTCs recommends driving normally for several days and leaving the car parked overnight between journeys.[1]
Is it always the cap?
It is the most common cause and the first thing to test. AutoDTCs estimates that a new cap resolves between 30 and 40% of cases with original caps that have many kilometres on them. If the code returns after a good-quality cap, the leak is elsewhere and the next step is the smoke test.[1][2]
How does it differ from P0442 and P0455?
In the size of the leak the control unit detects: P0456 is the smallest, P0442 a small one and P0455 a large one. Samarins notes that P0456 often appears together with P0455.[1][3]
Will I pass the MOT with code P0456?
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.
- P0456: Evaporative Emission System Leak Detected, Very Small LeakAutoDTCs · Technical documentation · consulted 31 October 2026
- 16840/P0456/001110 - EVAP System: Very Small Leak DetectedRoss-Tech Wiki · Technical documentation · consulted 31 October 2026
- P0455 Evaporative Emission Control System Leak Detected (Large leak)Samarins.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