Diagnostic code · Emissions / EVAP

Honda P0455 Code: Large EVAP Leak — Causes & Fix

Updated October 8, 2026Sources

On this page 4 sections

Meaning: A large leak in the EVAP (evaporative emissions) system: fuel vapor is escaping instead of staying sealed in.
Checks to start with: The gas cap — loose, missing, or the wrong cap.
Safe to drive?: If the light is steady, Honda says to avoid high speeds and have the vehicle inspected immediately. If it starts flashing, stop safely. It also won't pass emissions.

Before paying for any diagnosis, tighten or replace the gas cap and drive for several days — a loose or worn cap is one 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 traps fuel vapor from the tank and routes it back to the engine to be burned. 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.

Start with the simplest possible cause: a loose, missing, or worn gas cap. Tighten it until it clicks (or fit a new OEM cap) and drive for several days 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).

Possible causes

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 for several 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.

FAQ

What does the P0455 code mean on a Honda?

P0455 means the engine computer has detected a large (gross) leak in the evaporative emissions (EVAP) system. Fuel vapor is escaping instead of being sealed in and routed back to the engine to be burned. On a Honda, possible causes include 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 simplest thing to rule out, so check it first — tighten it until it clicks or replace it, then drive for several days. 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?

If the check engine light is steady, Honda says to avoid high speeds and have the vehicle inspected immediately. If the light starts flashing, stop safely. With P0455 the system is venting a small amount of fuel vapor. The car won't pass an emissions test until it's fixed, and a lit EVAP code can mask a second EVAP problem as it develops.

What is the difference between P0455, P0456, and P0457?

They belong to the same family of EVAP leak codes, sorted by size and source. P0455 is a large leak, P0456 is a small leak, and P0457 is a leak traced specifically to a loose or missing fuel cap. With all three, start by checking the gas cap.

Sources

Owner's manual references are to the model and year named above. Wording and procedures can differ on your Honda, so check your own owner's manual.

How we source and correct →