P0456: Evaporative Emission System: Very Small Leak
Low SeveritySafe to drive (short-term)EVAP System
P0456 means the engine control unit has detected a very small leak in the evaporative emission control system - smaller than 0.020 inches (0.5mm). This is the smallest leak the OBD-II system can detect. The cause is almost always a fuel cap that was not tightened to the full click, a hardened cap rubber seal, or a hairline crack in a vapour line.
Estimated repair costFrom €10 to €550+, varies by vehicle
What does P0456 mean?
P0456 means the engine control unit has detected a very small leak in the evaporative emission control system - smaller than 0.020 inches (0.5mm). This is the smallest leak the OBD-II system can detect. The cause is almost always a fuel cap that was not tightened to the full click, a hardened cap rubber seal, or a hairline crack in a vapour line.
P0456 is a evap system-related diagnostic trouble code classified as low severity. When your vehicle's ECU detects this condition, it stores P0456 and illuminates the check engine light.
What are the symptoms of P0456?
If your vehicle has triggered P0456, you may notice one or more of these symptoms:
Check engine light on (often the only symptom)
Occasional faint fuel odour near the rear of the car, especially in warm weather
Fuel cap warning indicator on some vehicles (Ford, GM)
No driveability issues, normal fuel economy
Code may come and go between drive cycles before setting permanently
What causes P0456?
Here are the most common causes of P0456, ranked by how likely they are to be the culprit:
highFuel cap not tightened to the full click after refuelling
highHardened or cracked rubber seal on the fuel cap
mediumHairline crack in an EVAP vapour line, often where it bends near the fuel tank
mediumPurge or vent valve with a leaking internal seal (not stuck open, just weeping)
lowCracked or porous charcoal canister
lowLeak at the fuel filler neck rubber gasket
Is it safe to drive with P0456?
Generally yes, for short-term driving. A very small EVAP leak does not affect engine performance or safety. You can drive normally, but the check engine light will trigger an automatic fail at any EU vehicle inspection (TÜV, ITV, TA, SKP, MOT) until it is fixed.
How do you diagnose P0456?
Follow these steps to pinpoint the root cause of P0456:
Tighten the fuel cap until you hear three clear clicks. Clear the code and complete three full drive cycles (cold start to full operating temperature, then cool down) before checking if it returns. EVAP monitors only run under specific temperature and fuel-level conditions
Inspect the fuel cap rubber seal. If the seal is dry, glossy, cracked, or has lost flexibility, replace the cap. A worn seal is the second most common cause of P0456 after a loose cap
Perform a smoke test on the EVAP system with the fuel cap installed. A very small leak will appear as a faint, slow plume of smoke. Focus on hose connections, the purge and vent valve bodies, and the canister housing
Use a propane enrichment test on suspect joints. With the engine idling, slowly direct propane near each EVAP component. If the engine RPM rises, propane is entering through a leak
Command the purge valve closed with a bidirectional scan tool and pull vacuum on the EVAP system. The valve should hold vacuum for at least 30 seconds. A slow leak past the valve seat is a common P0456 cause
Test the vent valve in the same way. The vent valve must seal completely during the EVAP self-test. A weeping vent valve seal will not stick open enough to cause P0446, but is loose enough to fail the very small leak threshold
How much does P0456 cost to fix?
Repair costs for P0456 vary depending on the root cause and your vehicle. Here are typical estimates:
Repair
Parts Cost
Labor Cost
Total Estimate
DIY Difficulty
Replace fuel cap
€10–€40
€0–€0
€10–€40
Easy
Replace a cracked EVAP vapour line section
€15–€60
€40–€150
€55–€210
Moderate
Replace purge valve
€25–€120
€40–€150
€65–€270
Moderate
Replace vent valve
€30–€130
€60–€200
€90–€330
Moderate
Replace charcoal canister
€70–€300
€80–€250
€150–€550
Moderate
Prices estimated as of March 2026. Costs vary by region, vehicle, and shop.
P0456 on specific vehicles
P0456 behaves differently depending on your vehicle. Select your car below for model-specific causes, known issues, and adjusted cost estimates:
P0456 on BMW 3 Series
BMW 3 Series • 2006-2024
BMW 3 Series and 1 Series with the DMTL pump (Diagnostic Module Tank Leakage, fault code 2A17 on the BMW side) commonly throw P0456 when the DMTL pump motor or its rubber filter fails. The pump is mounted near the charcoal canister and is exposed to road debris. Replacement of the entire DMTL module is the typical fix. Fuel cap is rarely the cause on modern BMWs because the cap is integrated and tamper-resistant.
What causes P0456 on a BMW 3 Series?
BMW 3 SeriesDMTL pump motor or rubber filter failure (BMW fault code 2A17)
BMW 3 SeriesCracked EVAP line near the fuel filler neck
P0456 repair cost for BMW 3 Series
Estimated costs for BMW 3 Series ownersadjusted higher than average due to BMW-specific parts pricing
Repair
Parts Cost
Labor Cost
Total Estimate
DIY Difficulty
Replace fuel cap
€13–€52
€0–€0
€13–€52
Easy
Replace a cracked EVAP vapour line section
€20–€78
€52–€195
€72–€273
Moderate
Replace purge valve
€33–€156
€52–€195
€85–€351
Moderate
Replace vent valve
€39–€169
€78–€260
€117–€429
Moderate
Replace charcoal canister
€91–€390
€104–€325
€195–€715
Moderate
Prices estimated as of March 2026. Costs vary by region, vehicle, and shop.
P0456 on Volkswagen Golf
Volkswagen Golf • 2005-2024
The Golf shares EVAP architecture with the rest of the VAG range. The N80 purge valve is the most common P0456 trigger on Mk6, Mk7, and Mk8. On the 1.2 TSI and 1.4 TSI engines, the valve weeps internally rather than sticking, so it tests fine with a multimeter but fails a vacuum hold test. The fuel cap on Mk7+ is integrated with the filler neck and rarely causes leaks.
Volkswagen GolfCracked carbon canister housing on Mk6
P0456 repair cost for Volkswagen Golf
Estimated costs for Volkswagen Golf ownersadjusted higher than average due to Volkswagen-specific parts pricing
Repair
Parts Cost
Labor Cost
Total Estimate
DIY Difficulty
Replace fuel cap
€12–€46
€0–€0
€12–€46
Easy
Replace a cracked EVAP vapour line section
€17–€69
€46–€173
€63–€241
Moderate
Replace purge valve
€29–€138
€46–€173
€75–€311
Moderate
Replace vent valve
€35–€150
€69–€230
€103–€379
Moderate
Replace charcoal canister
€81–€345
€92–€288
€173–€633
Moderate
Prices estimated as of March 2026. Costs vary by region, vehicle, and shop.
P0456 on Toyota Camry
Toyota Camry • 2007-2024
Toyota EVAP systems set P0456 most often from a loose or hardened fuel cap. The 2007-2017 Camry uses a screw-on cap that is particularly sensitive to seal age - replace the cap every 4 to 5 years preventively. From 2018 the Camry switched to a capless filler that eliminates this failure mode entirely.
What causes P0456 on a Toyota Camry?
Toyota CamryHardened fuel cap seal on 2007-2017 models
Toyota CamryCharcoal canister cracking after 200,000 km
P0456 on Honda Civic
Honda Civic • 2006-2024
Civic EVAP systems are robust. P0456 on a Civic is most often a fuel cap issue or a cracked vapour line near the rear axle. The 2016+ 1.5L turbo has a known issue where the EVAP canister vent solenoid filter clogs with road debris, causing the valve to seal imperfectly and producing intermittent P0456 codes. Honda has revised the filter design twice.
What causes P0456 on a Honda Civic?
Honda CivicVent solenoid filter clog on 1.5T (2016+)
Honda CivicVapour line damage at the rear axle area from underbody work
P0456 repair cost for Honda Civic
Estimated costs for Honda Civic ownersadjusted lower than average due to Honda-specific parts pricing
Repair
Parts Cost
Labor Cost
Total Estimate
DIY Difficulty
Replace fuel cap
€9–€36
€0–€0
€9–€36
Easy
Replace a cracked EVAP vapour line section
€14–€54
€36–€135
€50–€189
Moderate
Replace purge valve
€23–€108
€36–€135
€59–€243
Moderate
Replace vent valve
€27–€117
€54–€180
€81–€297
Moderate
Replace charcoal canister
€63–€270
€72–€225
€135–€495
Moderate
Prices estimated as of March 2026. Costs vary by region, vehicle, and shop.
Related diagnostic codes
These codes are often seen alongside P0456 or indicate related issues:
Indefinitely from a mechanical safety standpoint. P0456 only affects emissions, not engine operation. However, the check engine light will fail any EU emissions inspection. Plan the repair before your next TÜV, ITV, TA, SKP, or MOT date.
Will P0456 cause my car to fail TÜV or other EU inspections?
Yes. Every EU technical inspection regime fails a vehicle with an active check engine light, regardless of the underlying code. The pre-inspection OBD readiness check will also catch a recently cleared P0456 because the EVAP monitor takes 3 to 5 drive cycles to complete.
Will P0456 affect my fuel economy?
No, not in any measurable way. The leak is smaller than 0.5mm. The amount of fuel vapour escaping is too small to register on your trip computer. If you are also seeing reduced fuel economy, look for another cause like a faulty oxygen sensor or air leak.
Can hot or cold weather trigger P0456?
Yes. The EVAP monitor compares pressure changes in the fuel system to ambient temperature. Sudden cold snaps can shrink rubber seals just enough to leak below the small-leak threshold. Hot weather can vaporise fuel faster than a marginal canister or valve can handle. P0456 codes that appear only in winter are often a stiffening fuel cap seal.
Why does P0456 keep coming back after I tighten the cap?
Three possibilities. First, the cap seal has hardened and tightening alone is not enough - replace the cap. Second, there is a second leak elsewhere in the system that needs a smoke test to find. Third, on some Toyota and Subaru models the EVAP test parameters are sensitive enough that a slightly degraded purge valve seal will set P0456 even with a perfect cap.
