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What it meansA large leak in the EVAP (evaporative emissions) system — fuel vapor is escaping instead of staying sealed.
Most likely fixA loose, missing, or wrong gas cap — check it first.
Safe to drive?Yes — it won't affect how the car runs, but it won't pass emissions.
Typical cost$0–$350 (gas cap vs. EVAP vent valve).
Before paying for any diagnosis, tighten or replace the gas cap and drive a day or two — a loose or worn cap is the single most common cause of P0455, and the code can clear on its own once the system reseals.
What P0455 means
P0455 stands for “Evaporative Emission System Leak Detected (Large Leak).” Your Honda’s EVAP system is supposed to trap the fuel vapor from the tank and route it back to be burned — and to do that it has to stay completely sealed. When the engine computer runs its leak test and finds a large leak, it sets P0455 and turns on the check engine light. On many Hondas the same fault may also show as the Check Emission System message.
The reassuring part: P0455 is almost never an engine problem. The most common cause by far is the simplest one — a loose, missing, or worn gas cap. Tighten it until it clicks (or fit a new OEM cap) and drive for a day or two before assuming anything more expensive.
If a known-good cap doesn’t clear it, the leak is elsewhere in the system: a cracked vapor hose, a stuck-open EVAP vent valve, or a cracked charcoal canister. Because a large leak can be hard to see, a smoke test is the fastest way to pinpoint it. The closely related codes are P0456 (a small EVAP leak) and P0457 (a leak traced specifically to the fuel cap).
Common causes most common first
Loose, missing, or non-spec gas cap
Cracked or disconnected EVAP hose / vapor line
Stuck-open EVAP vent valve (canister vent)
Purge valve stuck open
Cracked charcoal (EVAP) canister
Leak at the fuel filler neck or tank seal
Do these checks first
Re-seat the gas cap until it clicks (or fit a new OEM cap), then drive 1–2 days to see if the code clears on its own.
Inspect the EVAP hoses and the filler neck for cracks, splits, or a disconnected line.
Smoke-test the EVAP system to pinpoint a large leak you can't see.
Check the EVAP vent and purge valves — a vent valve stuck open mimics a large leak.
A gas cap is $0–$20 (often free if it just needed tightening). An EVAP vent or purge valve is typically $120–$350 installed; a cracked canister or filler neck can run more.
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FAQ
What does the P0455 code mean on a Honda?
P0455 means the engine computer detected a large (gross) leak in the evaporative emissions (EVAP) system — fuel vapor is escaping instead of being sealed and routed back to be burned. On a Honda it most often points to the gas cap, a cracked vapor hose, or a stuck-open EVAP vent valve.
Is P0455 always the gas cap?
No, but the gas cap is the most common single cause, so check it first — tighten it until it clicks or replace it, then drive a day or two. If the code returns with a known-good cap, the leak is elsewhere, such as a cracked EVAP hose or a stuck vent valve, and needs a smoke test to find.
Can I drive my Honda with a P0455 code?
Yes. A P0455 EVAP leak doesn't affect how the engine runs, your safety, or fuel economy in any meaningful way — you're only venting a small amount of fuel vapor. The catch is the car won't pass an emissions test until it's fixed, and a lit EVAP code can hide a second EVAP problem developing.
What is the difference between P0455, P0456, and P0457?
They're the same family of EVAP leaks, graded by size and source. P0455 is a large leak, P0456 is a small leak, and P0457 is a leak specifically traced to a loose or missing fuel cap. All three start with checking the gas cap.
How much does it cost to fix a P0455 on a Honda?
If it's the gas cap, it's $0–$20. If a smoke test finds a stuck EVAP vent valve, purge valve, or cracked hose, expect roughly $120–$350 installed. A cracked charcoal canister or filler neck repair costs more.