P0456 on Honda: How to Diagnose & Fix
Evaporative Emission Control System Leak Detected (Very Small Leak)
2 Honda models · 2 documented issues · $25-$400 repair
P0456 on Honda by model: symptoms, diagnosis and fix
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.
Common Symptoms
- Check engine light on
- Occasional faint fuel odor
- No drivability change
- Code often returns after refueling
- Sometimes paired with 'check fuel cap' message
How to Fix
Start with the cheapest fix: inspect and replace the OEM fuel cap (Honda P/N 17670-SDA-A02 family) with a genuine Honda cap, then clear the code and drive several drive cycles. If it returns, perform an EVAP smoke test to pinpoint the leak; the usual repair is replacing the canister purge valve (engine bay) or the vent solenoid (under the car near the charcoal canister). Avoid aftermarket gas caps, which commonly reseal poorly.
What you need to fix it
Only diagnosis- and fitment-reviewed repair parts are linked here.
- Honda 17670-SDA-A01 fuel-filler capOEMHonda 17670-SDA-A01
The catalog shows broad 2003-2004 coverage but narrower 2005 coverage; use VIN confirmation for 20
- Honda 17670-SHJ-A02 fuel-tank capOEMHonda 17670-SHJ-A02
Replace a confirmed failed cap on the later seventh-generation branch Fitment/availability: Selected 2005-2007 Accord configurations; supersedes 17670-SHJ-A01 and 17670-SHJ-A31.
- Honda 17670-T3W-A01 complete fuel-filler capOEMHonda 17670-T3W-A01
Replace a confirmed failed cap-seal branch on the eighth- or ninth-generation car Fitment/availability: 2008-2017 Accord L4 or V6 in the seller's listed US configurations.
As an Amazon Associate, we earn from qualifying purchases; other part links may also earn au7o a commission. Confirm fitment by VIN before buying.
Sources for this issue (1)
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.
Common Symptoms
- Check Engine Light on
- Difficulty filling the fuel tank / pump clicks off early (stuck-closed vent valve)
- Occasional fuel odor
- Code appears right after refueling
- Fails emissions/smog readiness
How to Fix
Inspect and re-seat the gas cap first; on older Civics replace a worn cap with a genuine Honda unit (e.g., OEM 17670-series). On 2016+ capless systems, make sure the filler flap fully closed and nothing is caught in it. If the leak persists, smoke-test the EVAP system: the two prime suspects are the purge solenoid (on the intake manifold — if you can blow through it freely it is stuck open and must be replaced) and the canister vent solenoid near the charcoal canister/tank. Replace whichever component fails the smoke/blow test and re-run drive cycles to confirm readiness.
What you need to fix it
Only diagnosis- and fitment-reviewed repair parts are linked here.
- Genuine Honda 17670-T3W-A01 fuel-filler capOEMHonda 17670-T3W-A01
Capped-system replacement only when the cap seal or ratchet fails inspection Fitment/availability: Honda catalog fitment for capped 2006-2015 Civic applications; supersedes 17670-SNA-A02 and 17670-TR0-A01/A11. Enter VIN.
As an Amazon Associate, we earn from qualifying purchases; other part links may also earn au7o a commission. Confirm fitment by VIN before buying.
Sources for this issue (3)
P0456 code reference
General diagnostic-code context. The code alone does not confirm a cause for your vehicle; use the applicable issue card and its sources.
Frequently asked questions
What does P0456 mean on a 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 it is documented across 2 models: Accord, Civic.
What are the most common causes of P0456?
The most common causes of P0456 are: 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. The specific cause varies by vehicle.
How much does it cost to fix P0456 on a Honda?
Published repair estimates on Honda range from $25 to $400 depending on the model and root cause. If an issue mentions a recall or campaign, check your VIN with the manufacturer or NHTSA and confirm eligibility and coverage with a dealer.
Looking for P0456 on a different make?
View P0456 across all makes →Content compiled with AI assistance using NHTSA complaints, TSBs, and owner reports. May contain errors. Always verify with your vehicle's service manual.