P0456 on Honda
Evaporative Emission Control System Leak Detected (Very Small Leak)
P0456 on Honda vehicles indicates evaporative emission control system leak detected (very small leak). Au7o has documented this code across 2 Honda models — most commonly on Accord, Civic. This emissions code means the evaporative emission (EVAP) control system has detected a very small leak — even tinier than the one flagged by P0442, roughly equivalent to a 0.020-inch hole. The EVAP system traps fuel vapors from the tank and prevents them from escaping into the atmosphere, and the computer tests for leaks by sealing the system and watching for pressure or vacuum loss. Because the leak is so small, the cause is often subtle, but a loose or worn gas cap is still the most common and easiest to check. It generally indicates a minor seal, hose, or valve leak somewhere in the fuel vapor system. Typical repair costs on Honda range from $25 to $400, depending on the specific model and root cause.
Common Causes of P0456
- •Loose, worn, or faulty gas cap or cap seal
- •Cracked or loose EVAP hose or line
- •Leaking vent valve or purge valve not sealing
- •Damaged O-ring or seal at the fuel filler neck
- •Small crack or leak in the charcoal canister
- •Leaking fuel tank or sending unit gasket
- •Loose or corroded EVAP component connection
P0456 on Honda by Model
Honda Accord(1 issue)
- P0442 — Small EVAP Leak from Degraded Fuel Cap Seal or Failing Purge Valve2003-2017
On the Honda Accord, P0442 (small EVAP leak) is one of the most common check-engine triggers and almost always traces to one of three components in order of likelihood: the fuel cap, the engine-bay canister purge valve, or the under-car canister vent solenoid. The gas cap's rubber O-ring hardens, cracks, and stops sealing with age (aftermarket caps are a frequent repeat offender on this model). When the cap is good, the electric canister purge valve (which sticks or leaks internally) and the vent solenoid are the next suspects. A common Honda giveaway is a P1457 or P0451/P0456 stored alongside P0442, which points to the canister vent-side hardware rather than the cap. Because the leak is small, it is often intermittent and may set after refueling.
Honda Civic(1 issue)
- P0455 — Gross EVAP Leak from a Failed Gas Cap or Stuck-Open Purge/Vent Valve2006-2024
P0455 indicates a large (gross) leak in the evaporative emission system — the PCM cannot build or hold EVAP vacuum/pressure at all. On the Honda Civic the two most frequent causes are strikingly simple: a gas cap that no longer seals (missing, loose, or a badly degraded O-ring) and the canister purge solenoid valve sticking open. On the 8th-gen (2006-2011) Civic the purge valve is mounted right on the intake manifold and a stuck-open valve is a documented failure. A stuck canister vent valve is another common source and can also cause a symptom drivers notice — difficulty pumping fuel / the pump clicking off early. On 10th- and 11th-gen (2016+, and especially capless-fill 2022+) Civics, the capless filler not fully closing after fueling has triggered P0455/P0456 EVAP leak codes.
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View P0456 across all makes →Frequently Asked Questions
What does P0456 mean on Honda?▼
P0456 stands for "Evaporative Emission Control System Leak Detected (Very Small Leak)." This emissions code means the evaporative emission (EVAP) control system has detected a very small leak — even tinier than the one flagged by P0442, roughly equivalent to a 0.020-inch hole. The EVAP system traps fuel vapors from the tank and prevents them from escaping into the atmosphere, and the computer tests for leaks by sealing the system and watching for pressure or vacuum loss. Because the leak is so small, the cause is often subtle, but a loose or worn gas cap is still the most common and easiest to check. It generally indicates a minor seal, hose, or valve leak somewhere in the fuel vapor system. On Honda specifically, this code is documented across 2 models.
What causes P0456 on Honda vehicles?▼
Common causes on Honda: Loose, worn, or faulty gas cap or cap seal, Cracked or loose EVAP hose or line, Leaking vent valve or purge valve not sealing, Damaged O-ring or seal at the fuel filler neck, Small crack or leak in the charcoal canister. Specific causes vary by model and year — see the per-model sections below.
How much does it cost to fix P0456 on a Honda?▼
Repair costs on Honda range from $25 to $400, depending on the specific model and root cause.
Which Honda models have P0456 documented?▼
Au7o has documented P0456 on 2 Honda models: Accord, Civic.