What this code generally means, its most common causes, and how serious it is.
TYPE: GENERICSYSTEM: CATALYST AND EMISSIONS
What does the code P0455 mean?
Like P0442, this code comes from the EVAP system's leak test — but here the detected leak is large, often big enough to find without specialized equipment.
Common possible causes
A missing, loose, or damaged gas cap— the most common and easiest cause to check — look here first.
A disconnected or split EVAP hose— a visible disconnection rather than a fine crack.
A cracked charcoal canister— less common, but possible with age or an impact.
General severity
Generally minor for driving — check the gas cap
Despite the word "large," this code is still almost always not a driving risk — it's about the size of the vapor leak, not mechanical severity. Checking the gas cap is still the first move, free and quick.
⚠️This is still a general severity for this code, not a diagnostic for your car. Only a real read of your codes, with your mileage and vehicle history, can tell what's really going on.
Get a diagnostic for YOUR car
Connect a Bluetooth OBD2 reader and read your vehicle's real codes with Meca — free, no appointment, with causes ranked for your actual situation.
Meca doesn't replace an in-person check by a professional. For any serious sign (a flashing light, a major loss of power, a fuel smell), see a mechanic promptly.
Frequently asked questions
Did I forget to tighten the cap after filling up?›
That's the single most common cause of this specific code — check it first before looking at anything else.
Does "large leak" mean it's urgent?›
No — it describes the size of the vapor leak the test detected, not a driving danger. It isn't comparable to a liquid fuel leak.
How long before the light turns off after the fix?›
As with other EVAP codes, it usually takes several drive cycles before the system confirms the repair and clears the code on its own.