P0456

EVAP System Leak Detected (very small leak)

Evaporative emissions (EVAP) Generic OBD-II Low

What it means

P0456 means the ECM detected a very small leak in the evaporative emissions system, which captures fuel vapour from the tank and routes it to the engine. It doesn't affect how the car drives. The usual cause is a loose or worn gas cap, followed by a small hose, seal, or valve leak.

Low

Can I keep driving? Safe to keep driving — this is an emissions leak that doesn't affect how the engine runs; just fix it to pass inspection and stop the light.

Real-world scan data

Seen in

1,430

scans in the past year

Found in

0.2%

of scans

Appears alongside · share of P0456 scans

P0455in 12.4% of scans

P0457in 12.2% of scans

P0420in 12.0% of scans

Figures reflect only diagnostic scans recorded through our own apps and tools. Cars are typically scanned because a symptom or warning light prompted it, so these counts describe our scan records — not the incidence of faults in any model, and not the quality, reliability, or safety of any vehicle. No comparison between manufacturers or models is implied. All trademarks belong to their respective owners; no affiliation or endorsement is implied.

Common symptoms

What you'll notice

Check-engine light on (usually the only sign)
Occasionally a faint fuel-vapour smell near the tank
May fail an emissions/smog test

Common causes

Most likely first

Loose, worn, or wrong gas cap (most common — check this first)Likely
Cracked or disconnected EVAP hose or a hardened sealCommon
Leaking or damaged charcoal canisterCommon
Faulty purge or vent valve not sealingLess often

How to diagnose & fix

Work through it in order

Inspect the gas cap and its seal; retighten until it clicks or replace it, then clear the code and drive a few cycles.
Check the EVAP hoses and quick-connects from the tank to the canister for cracks or looseness.
If it recurs, use an EVAP smoke test to pinpoint the very small leak.
Inspect the charcoal canister and the purge and vent valves for leaks or a valve stuck slightly open.
Repair or replace the leaking component, then clear and let the EVAP monitor re-run.

P0456 by make

Based on commonly reported failure patterns across owner and repair communities, not on our scan data.

Ford

On Ford vehicles, a very small EVAP leak often comes from the gas cap, the filler neck or the vent and purge valves. A smoke test finds it faster than swapping parts.

Honda

Commonly reported on Hondas, where a very small EVAP leak can come from the gas cap, the canister vent shut valve or small cracked hoses. It is a hard leak to find by eye, so a smoke test saves guessing.

Toyota

Commonly reported on Toyotas, where a very small leak can come from a cap that no longer seals, a cracked EVAP hose or the canister area. Replacing the cap is a cheap first step.

Volkswagen

On VW and Audi models, the purge valve and small EVAP hose cracks are common sources of very small leaks. A smoke test is the reliable way to find it.

FAQ

Quick answers

Is it safe to drive with P0456?+

Yes. A very small EVAP leak doesn't affect drivability or safety; it only means fuel vapour is escaping, so fix it at your convenience.

Can I just clear P0456?+

You can, and if it was only a loose gas cap it may not return. If the leak is still there, the code comes back after the monitor re-runs.