What it means
The EVAP monitor detected a very small leak. The leak threshold and test method vary by vehicle; possible sources include a fuel-cap seal, hose, or valve.
At a glance
- Usually lights the check-engine light
- Affects emissions; the car can fail an emissions test
How it works
The EVAP system stores fuel vapor in a charcoal canister and routes it to the engine for burning; its valves and sealed hoses let the control module test for leaks. P0456 means the monitor found a leak small enough to fall in the very-small-leak category, such as a poor cap seal, slightly leaking valve, or hairline hose crack.
Common causes
Most likely first.
- Fuel cap seal hardened or worn
- Purge or vent valve leaking slightly
- Hairline crack in EVAP hose
Symptoms
- Check engine light on
- Possible smell of fuel near tank or engine bay
- Failed emissions inspection
- Loose-cap warning may appear
How to diagnose it
- Review the freeze-frame and EVAP monitor information to confirm the very-small-leak result and note whether the fuel cap was recently handled.
- Remove and inspect the fuel cap and filler-neck sealing surface for dirt, damage, a worn seal, or signs the cap was not seated.
- Visually inspect accessible EVAP hoses and connections for fine cracks, loose joints, or damage, paying attention near the tank and canister.
- Use the manufacturer's EVAP leak-test procedure, such as a suitable smoke test, to locate leaks too small to see during a visual check.
- If no leak is found, test the purge and vent valves for slight leakage using the specified procedure before replacing parts.
Common fixes
- Clean the filler-neck sealing surface and refit the cap correctly.
- Replace a fuel cap with a damaged or hardened seal.
- Repair or replace a cracked EVAP hose or loose connection.
- Replace a purge or vent valve if it fails the manufacturer's leak test.
Can I keep driving?
You can generally drive normally, but the small leak can allow fuel vapor to escape and may cause an emissions-test failure. If fuel odor becomes strong or you find liquid fuel, stop and have the leak addressed.
A code shows where the control module detected a fault, not always which part failed. Check the causes in order and confirm with a test before replacing parts. Have several codes? Check them together
This is a generic code: it means the same on every make. The car’s maker may add more detail in its own service information.