P0456 on a Honda: Causes, Fixes & Repair Cost

🟢 Low severity · drivable

Safe to drive — this is a tiny emissions leak, not an engine problem. Fix it before your next emissions test.

What P0456 means on a Honda

On a Honda, P0456 means the evaporative emission (EVAP) system has a very small leak. The system still runs, but your car will fail an emissions test until the leak is found, and an untightened gas cap is the most common trigger.

Is P0456 common on Hondas?

P0456 is common on Hondas like the Civic, Accord, and CR-V, and the gas cap is the first thing to check. Honda's EVAP system uses a vent shut valve and purge valve that can leak as they age. A smoke test finds the small leak when the cap is not the problem.

Commonly reported on: Civic, Accord, CR-V, Pilot.

Symptoms

Check engine light on
Usually no other symptoms
Occasional faint fuel smell

Common causes

most common: Gas cap not fully tightened or seal worn out
common: Tiny crack in an EVAP hose or O-ring
common: Failing purge valve or vent shut valve
less common: Very small crack in the canister or filler neck

How to fix it

Fix	DIY?	Typical cost
Tighten or replace the gas cap	Yes	$10–30
Inspect and replace cracked EVAP hoses	Yes	$10–60
Have a smoke test performed to find the exact leak	Mechanic	$50–150
Replace a faulty purge or vent shut valve	Yes	$30–150