P0456 means your car's fuel-vapor (EVAP) system found a very small leak when it ran its own leak test - California's OBD II rules require that test to catch a hole as small as 0.020 inch. The car drives normally; it will fail an emissions test while the light is on. The usual cause is the gas cap: tighten it until it clicks, look for a cracked or flattened seal, or fit a new cap, then drive normally for several days so the leak test can run again. If P0456 comes back, check the manufacturer bulletins further down (Hyundai, Acura, Volkswagen and Audi have issued them for some models) before paying for a smoke test to find the leak.
Also written as PO456 or P456.
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The EVAP (evaporative emission) system is the sealed set of hoses, valves and a charcoal canister that catches fuel vapor from the tank and lets the engine burn it instead of venting it. Every so often the engine computer seals that system and checks whether it holds pressure or vacuum. P0456 means the check found a very small leak - the smallest size it is designed to detect, often described as a pinhole. Because the leak is so small, the gas cap seal, a hairline crack in a hose, or a slightly seeping valve are the usual suspects. It has no effect on drivability but will keep the check-engine light on and fail an emissions test.
Yes, without any real time pressure. P0456 is the tightest leak the EVAP monitor can catch, and it has no effect at all on engine performance or safety. Drive normally and fix it before your next emissions test - start with the gas cap, since a worn seal there is the most common cause of this specific code.
Listed roughly most-likely first. Confirm with a scan tool and the freeze-frame data before replacing parts.
| Fix | DIY parts | At a shop |
|---|---|---|
| Replace the gas cap | $10 - $25 | $20 - $40 |
| Replace a seeping purge or vent valve | $20 - $80 | $100 - $300 |
| Replace the affected hose or canister | $30 - $200 | $150 - $500 |
Ranges are rounded and for the US market only - actual price depends on region, shop labor rates, and the exact make and model.
These open an Amazon search - add your year, make and model, because most of these parts are fitment-specific.
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P0456 is the very small EVAP leak threshold, roughly a 0.020 inch hole - half the size that triggers P0442 and about the diameter of a pin. This is the most frustrating code in the EVAP family precisely because the leak is too small to hear, see, or feel, and because the monitor that detects it is fussy about when it runs. Everything that causes P0442 causes this too, only less obviously. On many vehicles the leading cause is genuinely mundane: a gas cap that seals well enough for daily driving but not well enough for a test designed to find a pinhole.
A very small leak is the hardest EVAP fault to find, and for some models the carmaker has already found it. California's OBD II rules set the monitoring standard for detecting a leak as small as 0.020 inch, which is why a seal that looks fine can still set P0456. If your vehicle is on this list, the bulletin is the shortcut; if not, the steps above still apply.
Sources: Hyundai TSB 20-FL-003H (via NHTSA); Acura Service Bulletin 14-053 (via NHTSA); Volkswagen Technical Tip 20-23-01TT (via NHTSA); Audi TSB 2040924 (via NHTSA); CCR title 13, section 1968.2 (CARB OBD II requirements), via Cornell LII
This code is frequently misread as a failing fuel pump or a fuel delivery problem because it involves the tank. It is purely a vapor containment fault - it has no effect on how the engine runs, and no fuel system component is failing.
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Difficulty: Moderate to Hard. Time: 0.5 - 5 hours. DIY parts: $15 - $200. Shop total: $150 - $650.
Start by simply replacing the cap - that is a fifteen dollar, five minute job with a real chance of ending it. Beyond that, this code is genuinely hard to chase without proper equipment, and dropping a fuel tank to reach a sending unit seal is heavy, awkward work with fuel involved. This is the EVAP code where paying a shop is most often the rational choice.
Stop fueling past the first pump shutoff. Forcing in extra fuel pushes liquid into a canister built for vapor only, and a saturated canister leaks at exactly this threshold. It is the most preventable cause of the least findable EVAP code. Track your services in ServiceSage so when this code returns in two years you can see instantly what you already replaced and what you have not. Track this maintenance free.
Typical US independent-shop repair cost for P0456 runs about $20 - $500, depending on the root cause. Common fixes: Replace the gas cap (about $20 - $40 at a shop); Replace a seeping purge or vent valve (about $100 - $300 at a shop); Replace the affected hose or canister (about $150 - $500 at a shop).
Yes - a loose, cracked, or worn gas cap is the single most common cause of P0456. Before assuming a bigger EVAP leak, make sure the cap clicks fully tight, or just replace it since caps are cheap, then clear the code and see if it returns. If it does, the vent valve, purge valve, and hoses are the next things to check.
Often, if the leak was the gas cap seal and the new or reseated cap holds. California's OBD II regulation (13 CCR 1968.2, as written for 2004-2018 models) turns the check-engine light off after three driving cycles in a row in which the monitor that set it runs and no longer finds the fault, and lets the stored code be erased after 40 warm-up cycles without it. The catch is that the EVAP leak monitor only runs under particular conditions - temperature and a cold start among them - so it can take several days of normal driving. A scan tool's readiness screen shows whether the EVAP test has run since the fix; if it has run and P0456 is back, the leak is somewhere else.
All three mean the EVAP self-test found a leak; the number tells you how big. P0455 is a large leak (a missing or unsealed gas cap, a disconnected hose), P0442 is a small leak, and P0456 is a very small leak - the smallest the monitor is designed to catch, often described as a pinhole around 0.020 inch. The smaller the leak, the more likely it is a seal, a hairline-cracked hose, or a slightly seeping valve rather than something obviously broken.
Replace or inspect the gas cap first, then clear the code and drive normally for a few days. If P0456 returns, the reliable way to find a pinhole leak is a smoke test: low-pressure smoke is fed into the EVAP system and comes out wherever it leaks. Visual inspection alone rarely finds a leak this small. Many shops charge about one hour of diagnostic labor for a smoke test.
El código P0456 indica que el sistema de control de emisiones evaporativas (EVAP) detectó una fuga muy pequeña de vapores de combustible. No afecta el manejo del vehículo, pero mantiene encendida la luz de check engine y puede hacer que no pase la inspección de emisiones. La causa más común es un tapón de gasolina desgastado o mal cerrado; si el código regresa, una prueba de humo localiza la manguera, válvula o sello con fuga.
Related trouble codes: P0455 - EVAP System Leak Detected (Large Leak), P0442 - EVAP System Leak Detected (Small Leak), P0441 - Evaporative Emission System Incorrect Purge Flow, P0446 - Evaporative Emission System Vent Control Circuit Malfunction
Ford: Many Fords since the late 2000s use the capless Easy Fuel filler instead of a gas cap. There is nothing to tighten, so a very small leak there usually means dirt or damage at the filler flap seal - inspect and clean it before replacing EVAP valves, and use the funnel Ford supplies when filling from a can.
Chrysler, Dodge and Jeep: Many Chrysler-family vehicles use an evaporative system integrity module (ESIM) at the canister to run the leak test. A failed ESIM or its seal is a widely reported cause of P0456 on these vehicles once the cap has been ruled out.
Toyota and Honda: Both makes run a sensitive leak test, so a worn cap seal alone is enough to set P0456. If a new cap does not fix it, the vent valve or canister assembly under the car is the next check - a smoke test at the filler neck finds it faster than swapping parts.