P0456: Evaporative Emission System Very Small Leak Detected
The fuel vapor system has a very tiny leak.
Severity: 1 of 4
Safe to drive. It affects emissions, not engine operation. Repair it before your next inspection.
Estimate range covers the repairs listed below; see the cost breakdown. A flashing check engine light, a hot temperature gauge, or brakes that feel different mean stop driving and get help.
What P0456 means
P0456 flags a leak even smaller than P0442. The test is sensitive enough that a slightly worn cap seal or a tiny crack in a hose can trigger it.
These are among the hardest leaks to locate. Expect a smoke test if the cap is not the culprit.
Common causes (cheapest likely first)
- Gas cap seal. Replace with a quality cap.
- Tiny hose crack. Often near the tank.
- Purge or vent valve seal. Valves that leak slightly.
- Canister or filler neck seal. Less common.
Symptoms
- Check engine light
- No drivability symptoms
DIY difficulty: Moderate
Easy to try a new cap. Locating very small leaks needs a smoke tester.
Tools: OBD-II scanner, Gas cap, Smoke tester
Estimated repair cost
This is an estimate, built from typical parts price ranges plus labor hours times an assumed shop rate of $110 to $190 per hour. Actual prices vary by vehicle, region, and shop. Diagnosis fees are often extra.
| Repair | Parts | Labor | Estimate (low / high) |
|---|---|---|---|
| Gas cap | $10 to $35 | 0.0 to 0.1 h | $10 + 0.0 × $110 = $10 $35 + 0.1 × $190 = $54 |
| Smoke test diagnosis | $0 to $0 | 0.5 to 1.0 h | $0 + 0.5 × $110 = $55 $0 + 1.0 × $190 = $190 |
| EVAP valve or hose | $15 to $150 | 0.3 to 1.5 h | $15 + 0.3 × $110 = $48 $150 + 1.5 × $190 = $435 |
Watch a repair video
How to Find an EVAP Leak (P0440, P0442, P0455, P0456). Third-party video, loads from YouTube (privacy-enhanced mode) only when you press play. Procedures vary by vehicle. Search YouTube for “P0456 fix” videos.
P0456 by make
Brand specific notes: Toyota, Dodge. Other makes: the code works the same way; see all makes.
Repair manuals
Step-by-step service manuals with torque specs and wiring diagrams:
Haynes manuals Chilton manuals
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Related codes
Check for recalls
Before paying for a repair, enter your VIN in the NHTSA recall lookup. Emissions parts may also be covered by a federal emissions warranty; check your warranty booklet.
FAQ
Can I ignore P0456?
Mechanically yes in the short term, but the light hides any new problems and you will fail emissions tests.
Does weather affect P0456?
Temperature and fuel level change when the test runs, so the code may come and go.