Diagnostic code · Emissions / EVAP

Honda P0456 Code: Small EVAP Leak — Causes & Fix

Updated October 8, 2026Sources

On this page 4 sections

Meaning: A small leak in the EVAP (evaporative emissions) system: a tiny amount of fuel vapor is escaping from a system that should stay sealed.
Checks to start with: Check the gas cap seal first, then smoke-test the EVAP system.
Safe to drive?: If the light is steady, Honda says to avoid high speeds and have the vehicle inspected immediately. If it starts flashing, stop safely. It also won't pass emissions.

P0456 is a small leak, which makes it the hardest EVAP code to find by eye. The search still starts with the cap. Fit a new OEM gas cap and drive for several days; if the code returns, a smoke test is the only reliable way to pinpoint a leak this small.

What P0456 means

P0456 stands for “Evaporative Emission System Leak Detected (Small Leak).” Your Honda’s EVAP system traps fuel vapor from the tank and sends it back to the engine to be burned. To do that, it has to stay sealed. When the computer’s leak test finds a small leak, one too minor to see or hear, it sets P0456 and turns on the check engine light. On some Hondas the same fault may appear as the Check Emission System message.

Because the leak is so small, P0456 is the hardest of the EVAP codes to chase down, but the search still starts at the gas cap. A marginal gas cap seal that’s hardened with age is one possible cause, so fit a new OEM-spec cap and drive for several days first. If the code comes back with a known-good cap, the next step is a smoke test. That’s the only reliable way to find a leak this minor, whether it turns out to be a hairline crack in a vapor hose, a weeping valve seal, or a cracked charcoal canister.

The closely related codes are P0455 (a large EVAP leak) and P0457 (a leak traced specifically to the fuel cap).

Possible causes

Worn or marginal gas cap seal
Tiny crack or pinhole in an EVAP hose / vapor line
Leaking purge or vent valve seal
Loose or cross-threaded gas cap
Hairline crack in the charcoal (EVAP) canister
Filler-neck seal or O-ring weeping vapor

Do these checks first

Fit a new OEM-spec gas cap and drive several days — a marginal cap seal is one possible small-leak cause.
Smoke-test the EVAP system. For a leak this small, smoke is the only reliable way to find it.
Inspect EVAP hoses and valve seals for hairline cracks, especially where lines flex or connect.
Make sure the car completes its EVAP drive cycle so the code can actually clear after a repair.

FAQ

What does the P0456 code mean on a Honda?

P0456 means the engine computer detected a small (minor) leak in the evaporative emissions (EVAP) system, so a tiny amount of fuel vapor is escaping. Because the leak is small, it's the trickiest EVAP code to track down. The gas cap seal is the first thing to rule out.

Why is P0456 so hard to fix?

The leak can be too small to see or hear. A worn gas cap is the easiest thing to rule out. Beyond that, the only reliable way to find a leak this minor is a smoke test, which pressurizes the EVAP system and shows where smoke seeps out.

Can I drive my Honda with a P0456 code?

If the check engine light is steady, Honda says to avoid high speeds and have the vehicle inspected immediately. If the light starts flashing, stop safely. With a small EVAP leak, the system is venting a little fuel vapor. The car won't pass an emissions test until it's fixed, and a lit EVAP code can hide a second problem.

What is the difference between P0456, P0455, and P0457?

They're the same family of EVAP leaks, graded by size and source. P0456 is a small leak, P0455 is a large leak, and P0457 is a leak traced specifically to a loose or missing fuel cap. All three start with checking the gas cap.

Sources

Owner's manual references are to the model and year named above. Wording and procedures can differ on your Honda, so check your own owner's manual.

How we source and correct →