CarSense › Trouble codes › P0456

P0456: Evaporative Emission System - Very Small Leak Detected

What this check-engine code means in plain English, what usually causes it, and what a fix typically costs.

Severity: Monitor — not urgent, but should be addressed soon

What P0456 means

The engine computer has detected a very small leak in the evaporative emission (EVAP) system, which captures fuel vapors from the tank and prevents them from escaping into the atmosphere. The leak is typically equivalent to a hole about 0.020 inches in diameter, allowing fuel vapors to escape rather than being routed to the engine for combustion.

What causes P0456?

Likely
Loose or damaged gas capThe most common cause is a gas cap that is loose, cracked, or has a worn seal, allowing vapors to escape.
Likely
Cracked or disconnected EVAP hoseSmall rubber hoses in the EVAP system can crack, split, or become disconnected over time due to heat and age.
Possible
Faulty purge or vent valveThe purge valve or vent valve may be stuck open or leaking, allowing vapors to escape when they should be sealed.
Less common
Leak in charcoal canisterThe EVAP canister itself may have developed a crack or the seals may have deteriorated, creating a small leak point.

Is P0456 safe to drive?

Drive it?
Yes, safe to drive
Watch for
Fuel odor or decreased fuel economy
DIY-friendly?
Start by checking and tightening the gas cap; further diagnosis may require a smoke test.

This code does not affect driveability or safety, so you can continue driving normally. However, the vehicle will fail emissions testing in most areas, and you may notice a slight decrease in fuel economy or occasionally smell fuel vapors.

P0456 repair cost

~$50 – $400+

Industry-average estimates. Cost depends on the leak location; a new gas cap costs around $50, while replacing EVAP valves or hoses typically runs $150-$400 including diagnosis and labor.

Which one is it for your car?

Plug a cheap OBD2 adapter into your car and CarSense reads your codes and tells you the likely cause and a real cost for your exact vehicle — free to scan, no proprietary dongle.

Download for iPhoneGet it on Android

Related codes

P0442P0455