P0456 on a Subaru: Causes, Fixes & Repair Cost

🟢 Low severity · drivable

Safe to drive — a very small fuel vapor leak won't affect the engine, but fix it before an emissions test.

What P0456 means on a Subaru

On a Subaru, P0456 means the computer found a very small leak in the fuel vapor system. Subaru's EVAP system is sensitive, and a fuel cap left slightly loose is the classic trigger.

Is P0456 common on Subarus?

P0456 is a common sight on Outbacks, Foresters, and Crosstreks, usually after a fill-up. When the cap isn't the cause, a smoke test often finds tiny cracks in vapor hoses, which are common on older Subarus.

Commonly reported on: Outback, Forester, Impreza, Crosstrek.

Symptoms

Check engine light is on
No change in how the car drives
Occasional faint fuel smell

Common causes

most common: Fuel filler cap not fully tightened or worn seal
common: Cracked or loose EVAP vapor hose
common: Leaking EVAP purge valve
less common: Tiny leak at the fuel filler neck or canister

How to fix it

Fix	DIY?	Typical cost
Retighten the fuel cap until it clicks, then clear the code	Yes	$0–30
Have a smoke test performed to find the exact leak	Mechanic	$60–150
Replace a cracked EVAP vapor hose	Yes	$20–80