P0456 Code: Evaporative Emission System Leak Detected (Very Small Leak)

🟢 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

The evaporative emission (EVAP) system has a very small leak. It's the most sensitive EVAP leak code, often triggered by a gas cap that wasn't fully tightened or a tiny seal that isn't quite perfect.

Symptoms

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

Common causes

most common: Gas cap not fully tightened or seal wearing out
common: Tiny leak in an EVAP hose or O-ring
common: Faulty EVAP purge or vent 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 EVAP hoses and O-rings, replacing any that are cracked	Yes	$10–60
Have a smoke test performed to find the exact leak	Mechanic	$50–150
Replace a faulty purge or vent valve	Yes	$30–120

Frequently asked questions

Can I drive with a P0456 code?

Yes. It's a tiny emissions leak and won't affect drivability. Fix it before your next emissions test.

Is P0456 usually just the gas cap?

Very often, yes. An under-tightened or aging gas cap is the most common cause, so start there.

What's the difference between P0442, P0455, and P0456?

They're all EVAP leaks, just different sizes: P0456 is a very small leak, P0442 is a small leak, and P0455 is a large leak.

Related codes

P0442 Code: Evaporative Emission Control System Leak Detected (Small Leak)

P0455 Code: Evaporative Emission Control System Leak Detected (Large Leak)

P0440 Code: Evaporative Emission Control System Malfunction

P0456 by vehicle brand

Causes and repair costs for P0456 differ between makes. Pick your brand for the specifics.

P0456 on a Toyota

P0456 on a Honda

P0456 on a Ford

P0456 on a Chevy

P0456 on a Nissan

P0456 on a Mercedes-Benz

P0456 on a Volkswagen

P0456 on a Hyundai

P0456 on a Subaru

P0456 on a Mazda

P0456 on a Jeep

P0456 on a Lexus

P0456 on a Volvo

Related guide: How to Reset a Check Engine Light →

Updated 2026-08. This page is informational and not a substitute for professional diagnosis.