P0455 Code: Evaporative Emission System Large Leak Detected

What Is the P0455 Code?

The P0455 code is a common emission-related fault. It’s hard to miss once it triggers.

You might see it labeled differently. Like p0455 engine code, dtc p0455, or even eobd/obdii error p0455. All mean the same thing.

Technically, it stands for “Evaporative Emission Control System Large Leak Detected.” Let’s break that down.

Your car has an EVAP system. Its job? Trap fuel vapors. Stop them from leaking into the air.

When the system has a big leak—think a loose gas cap or cracked hose—the ECU notices. It sets dtc p0455 and turns on the false check engine light.

This isn’t a brand-specific code. Ford, Chevy, Toyota—any vehicle with OBD-II can show it.

Eobd/obdii error p0455 pops up because the EVAP system loses pressure. The ECU can’t maintain the tight seal it needs.

It’s not an emergency. But it matters. A large leak fails emissions tests. Wastes fuel, too.

So when you see p0455 engine code, know this: your EVAP system has a big leak.

using the Foxwell GT60 diagnostic scanner to diagnose a P0455 code

What is an EVAP System?

The EVAP system—short for Evaporative Emission Control System—is your car’s built-in “vapor trap.”

It stops fuel fumes from escaping into the air. That’s key for the environment. And for passing emissions tests.

Every gas-powered vehicle has one. It includes a few main parts: a gas cap, charcoal canister, hoses, and valves (like the purge and vent valves).

The gas cap seals the tank. The charcoal canister soaks up vapors when the car is off. Hoses carry vapors to the engine later, where they’re burned as fuel.

No EVAP system? Fuel fumes would pollute freely. And your car would fail every emissions check.

How Does the EVAP System Work in Relation to P0455?

The EVAP system relies on pressure. A tight seal keeps vapors in. When it breaks, dtc p0455 follows.

Here’s the link: The ECU runs tests on the EVAP system. It closes valves to trap pressure, then checks if that pressure holds.

If there’s a large leak—say, a cracked hose or loose gas cap—pressure drops fast. The ECU flags this as a failure.

That’s when eobd/obdii error p0455 pops up. It’s the system’s way of saying, “I can’t contain vapors anymore.”

Small leaks trigger other codes (like P0442). But p0455 engine code** means the leak is big enough to let significant fumes escape.

In short: The EVAP system’s job is to seal vapors. P0455 means that seal is badly broken.

What Are the Symptoms of a P0455 Code?

Most symptoms of dtc P0455 are subtle at first. But they’re worth noticing.

- Check engine light on. This is the first sign. It’s usually solid, not flashing. In many cases, drivers may not notice any change in engine performance, so the warning light is the primary clue.
- Fuel odor. A large leak lets fuel vapors escape. You might smell gas near the tank or even inside the car.
- Difficulty filling the tank or the fuel pump shutting off prematurely due to pressure issues.
- Decreased fuel efficiency as escaping vapors represent lost fuel.
- Failed emissions test. Vapors escaping mean high pollution levels. Tests will flag this, and you’ll need to fix dtc p0455 to pass.

Don’t ignore it—p0455 engine code rarely goes away on its own. The leak will only get worse over time.

What Are Some Causes of a P0455 Code?

Loose or broken gas cap: The top culprit. A cap not tightened all the way, or one with a worn rubber seal, breaks the system’s seal. Fixing this often clears p0455 engine code fast.
Cracked EVAP hoses: Hoses carry fuel vapors. Heat and age make them brittle. A split here lets pressure escape instantly—triggering p0455.
Faulty purge or vent valve: These valves control system pressure. A stuck vent valve can’t hold pressure. The ECU reads this as a big leak.
Leaking fuel tank or filler neck: Rust or bumps can crack the tank. Even a small hole counts as “large” for the EVAP system. Rare but possible, especially in older vehicles or after accidents.
Other EVAP components malfunctioning, like the charcoal canister or pressure sensor.

How Serious Is the P0455 Code?

The P0455 code is generally not an immediate safety risk, as it rarely affects engine performance. However, ignoring it can lead to:
First, environmental harm. Escaped fuel vapors pollute the air. They feed smog and harm air quality. That’s why the EVAP system exists.
Second, wasted money. Vapors leaking mean lost fuel. You’ll fill up more often. Over time, this adds up to extra costs.
Third, failed emissions tests. Most places require these for registration. eobd/obdii error p0455 guarantees a fail. No fix, no legal driving.
Worst of all, small issues grow. A loose cap might lead to a cracked hose. A faulty valve could ruin the charcoal canister. Fixing dtc p0455 early costs $20 (for a cap) instead of $600 (for a canister).

Can I Still Drive with the P0455 Code?

Yes, but only for a little while.
P0455 engine code won’t make your car die suddenly. If just the check engine light is on—no gas smell, no weird performance—you can drive to work or the shop.
But don’t drag it out. Risks pile up. A fuel odor means flammable vapors are near hot parts. That’s a fire risk.
Driving also lets the leak get worse. What starts as a loose cap could become a cracked tank if other parts fail.
How long is safe? A day or two, tops. Use that time to scan again (confirm it’s still p0455 engine code) and check the gas cap first.
If you smell gas or feel the car act off? Stop driving. Call a mechanic. P0455 isn’t worth risking safety for.

How Easy Is It to Diagnose a P0455 Code?

Diagnosing DTC P0455 is usually straightforward—even for beginner DIYers. It starts simple, and only gets trickier if the leak is hidden.

Grab an OBD-II scanner, such as the Foxwell NT909 or Foxwell GT60. Plug it in, and it will confirm P0455 engine code (or EOBD/OBDII error P0455) quickly. No guesswork here, and these scanners also provide live data for the EVAP system, making it easier to pinpoint the problem.

Check the easiest culprit: the gas cap. Is it loose? Cracked? Wiggle it—if it turns more than a half-turn, it wasn’t tight. A worn seal is easy to spot, too. This step takes 30 seconds.

If the cap looks good, inspect the EVAP hoses. Follow the lines from the gas tank to the engine bay. Look for cracks, dry rot, or disconnected ends. These hoses are often visible and accessible.

For harder-to-find leaks, use a spray bottle. Mix soapy water and spritz it on hoses, the filler neck, and valve connections. Turn the key to “on” (don’t start the engine)—bubbles mean a leak. This works for small cracks you might miss.

Professional mechanics use smoke machines. They pump smoke into the EVAP system; leaks puff out smoke clearly. This is fast, but only needed if DIY checks fail.

The best part? 80% of DTC P0455 cases trace to the gas cap or a cracked hose. No fancy tools required. With a Foxwell scanner, you can confidently diagnose these common issues before spending money on larger components like the fuel tank.

Foxwell NT909

Full-system diagnostics with complete OBD2 modes; one-click reading and clear display of DTC P0455 fault definitions
Includes 30+ reset functions, with built-in EVAP system testing
Compatible with multiple brands (Ford, Chevrolet, Toyota, Honda, and most mainstream vehicles)

Foxwell GT60

Full OBDII/EOBD functions with complete system diagnostics
Bi-directional control + live data stream
Includes 20+ maintenance functions, with built-in EVAP/Smog testing

How to Fix the P0455 Code?

In most cases, fixing a P0455 code doesn’t require replacing the entire fuel tank, even if that’s what some dealerships may suggest. The EVAP system has multiple components, and leaks are often caused by smaller, serviceable parts.

Common solutions include:

Tighten or replace the gas cap– A loose or cracked cap is the 1 cause of P0455.
Replace the fuel filler neck – If the filler neck or vent/overflow tube is cracked, it can trigger the code. Replacement usually costs around $120–$300 plus labor, much cheaper than a full tank replacement.
Use aftermarket or salvage yard parts – Many owners save money by sourcing used or non-OEM parts instead of buying a full fuel tank from the dealer.
Patch the tubing – Rubber hoses can often be patched easily. Hard plastic hoses are more difficult, but some mechanics can still repair them rather than replacing the whole tank.

Real-world note: On Reddit, a 2017 Honda Accord owner was quoted $4,500 for a new fuel tank due to a tiny pinhole in the EVAP vent tube. Other mechanics pointed out that this issue could often be fixed by replacing or patching the filler neck tubing for just a few hundred dollars. Checking small, inexpensive components like the pinhole should always be the first step before assuming a major repair.

What Does It Cost and How Long to Repair a DTC P0455?

Repair Type	Estimated Cost	Estimated Time	Notes
Loose or cracked gas cap	Under $20	About 5 minutes	Most common and easiest fix
Cracked fuel filler neck or vent/overflow tube	$120–$300 + labor	30–60 minutes	Aftermarket or salvage parts can reduce cost
Patching EVAP hoses	Varies; slightly higher than filler neck replacement	15–45 minutes	Rubber hoses are easier to patch; hard plastic hoses harder
Full fuel tank replacement	$4,000–$4,500	1.5–3 hours	Only needed if the tank itself is damaged
Most DTC P0455 repairs can be repairs range from $20–$400 when diagnosed correctly and resolved in under an hour for 80% of cases when diagnosed correctly.

Vehicle-Specific Notes

The P0455 code can appear on virtually any modern vehicle equipped with an EVAP system, but certain makes and models have known quirks:

Honda & Acura: Small pinhole leaks in the fuel filler neck or vent tubes are common.

Ford & Chevrolet: Gas cap issues are frequently reported, especially after long-term use.

Toyota & Lexus: Cracks in EVAP hoses around the charcoal canister are occasionally observed.

Nissan: Older models may develop leaks near the purge valve or vent solenoid.

Tip: Even within the same model, production year and engine type can influence the exact location of EVAP components. Always refer to your vehicle’s service manual or use a reliable Foxwell OBD2 scanner (e.g., Foxwell NT909 or GT60) to pinpoint the source of the leak.

FAQs:

Can a P0455 code cause other problems?

Generally, a P0455 code (indicating a large leak in the EVAP system) doesn't cause immediate engine damage. However, it can bring about several inconveniences for car owners. For example, it may lead to reduced fuel efficiency, cause emissions tests to fail, and trigger additional EVAP - related codes such as P0442.

What should I do if the P0455 code keeps coming back after I think I've fixed it?

If the code recurs, the root cause wasn’t fully resolved—take these steps:
Recheck your repair: If you replaced the gas cap, ensure it’s the correct OEM/aftermarket fit and tightly sealed. For hoses, inspect for unaddressed cracks or loose connections.
Scan for related codes: Use an OBDII scanner (e.g., Foxwell GT60) to check for additional DTCs (e.g., P0442 for small leaks) that might point to hidden issues.
Test the EVAP system: Use a scanner with EVAP test functionality or a smoke machine to pinpoint leaks you missed (e.g., in hard-to-reach hoses or the charcoal canister).
Inspect less obvious parts: Check the purge/vent valves, fuel tank pressure sensor, or filler neck for cracks—these are common "hidden" causes.

Can a loose gas cap really cause a P0455 code?

Absolutely—a loose or damaged gas cap is the 1 cause of P0455 (responsible for 40–50% of cases). Even a small gap can allow fuel vapors to escape, triggering the code.

How does a faulty gas cap cause P0455?

The EVAP system relies on a closed, pressure-tight loop to trap fuel vapors. A faulty gas cap (loose, cracked, or with a worn rubber seal) breaks this loop, allowing vapor to escape and causing the car’s computer to detect a large leak (P0455).

Will a P0455 code clear itself?

Rarely. Some codes may reset if the issue is intermittent, but a persistent leak(like a damaged cap, cracked hose, or faulty valve) usually requires inspection and repair,the code will not clear on its own. Driving without fixing it will likely cause the check engine light to return.

Can cold weather cause a P0455 code?

Yes. Cold weather itself doesn’t cause P0455, but it can exacerbate existing weak points in the EVAP system, leading the code to appear. Rubber hoses and gas cap seals harden and become brittle in cold temperatures, worsening small cracks or worn seals.Ice buildup (e.g., around the filler neck or vent valve) can block airflow temporarily, but this usually triggers a different code—P0455 in cold weather typically points to pre-existing damage that cold has made worse.