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
P0442 Code: Evaporative Emission Control System Leak Detected (Small Leak)
P0455P0455 Code: Evaporative Emission Control System Leak Detected (Large Leak)
P0440P0440 Code: Evaporative Emission Control System Malfunction
Updated 2026-08. This page is informational and not a substitute for professional diagnosis.