What does P0456 mean?
Evaporative Emission Control System — Very Small Leak Detected
Direct Answer
P0456 indicates a very small EVAP leak — under 0.020 inches. This is the hardest EVAP code to locate because the leak is tiny and often intermittent. A professional smoke test is almost always required to find it.
Common Symptoms
- ✓Check engine light on
- ✓May intermittently set and clear on its own
- ✓Failed emissions test
Common Causes
- 01Slightly loose gas cap seal
- 02Pinhole crack in an EVAP hose or fitting
- 03Tiny crack in the charcoal canister
- 04Leak at the vent valve or purge solenoid connections
How to Fix P0456
Replace the gas cap
At under $30, this is the cheapest first step. Even a cap that appears fine can have a subtle seal failure.
Professional smoke test
For a sub-0.020 inch leak, smoke testing is the only reliable way to find it. Expect to pay $75–$150 for diagnosis.
Frequently Asked Questions
Why does P0456 keep coming back after I fix it?
Very small leaks can be intermittent — seals expand and contract with temperature. If the code returns after a gas cap replacement, a professional smoke test is the next step to find the actual leak location.
Estimated Repair Cost
$15–$500
Gas cap: $15–$30. Diagnosis: $75–$150. Hose or seal repair: $100–$300.
Safe to Drive?
Yes — with caution
Completely safe to drive. This code will not cause any drivability issues.
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