P0455 Code: Large EVAP Leak Causes, Cost and Fix

A P0455 code, which a scan tool prints as diagnostic trouble code (DTC) P0455 and some owners write as PO455, is the "large leak" code of the evaporative emission (EVAP) system. That's the sealed loop of tank, filler neck, cap, hoses, valves and a charcoal canister that keeps fuel vapor out of the air.

The usual advice is the gas cap, and here it's genuinely the right first move, because a large leak is the kind a cap left open makes. The light can stay on even after the right repair, because the leak test has to run and pass on its own before it goes off.

What does a P0455 code mean?

P0455 means the fuel vapor system leaked too much to pass its test, and carmakers' bulletins call it the EVAP system large leak. The car seals the loop, watches whether it holds, and stores P0455 when it can't hold at all.

Any part of the loop can be the hole, which is why a cap and a canister set the same code. The smaller leaks cars must also detect, 0.040 and 0.020 inch, are covered on the P0442 and P0456 pages, and the whole family is mapped on the P0440 page.

Can you drive with a P0455 code?

Yes, unless one of the signs below shows up, because a vapor leak doesn't feed or stop the engine. You may fail an emissions test, and a stored code hides the next fault behind the same light.

The exceptions are signs of liquid fuel or a fault that reaches the engine. Leaking fuel is a fire risk, and a stall after filling up points to a line or valve fault, not a cap.

We'd stop driving and get it checked if:

• You smell gasoline. Especially inside the car. See car smells like gas.
• Fuel drips, pools or overflows at the filler. One owner reported fuel overflow at the filler neck.
• It stalls or won't start after a fill-up. A vapor line loose inside the tank can do this.

What are the symptoms of a P0455 code?

You may see only the check engine light, because the leak is vapor, not the fuel the engine runs on. Some cars also show a cap or fuel-fill message on the dash, which points you to the filler first.

Here's what owners describe in the federal complaints naming P0455:

• A fuel smell or vapors. Sometimes strong inside the car.
• A "check fuel fill inlet" message. On Ford-built cars.
• Trouble at or after a fill-up. A no-start or a hard start, or fuel overflowing at the filler neck.
• The light coming back after a repair. Including after a recall repair.

What causes a P0455 code?

Any opening in the loop big enough to stop it holding: the cap, the filler neck or fill pipe, a vapor line off its fitting, or a vent valve stuck open. Carmakers have filed fixes for all four, and several of their instructions say to find the leak before replacing anything. P0455 alone confirms none of them. Each has its own test to run before any part is bought.

Here are the four places the leak turns up, starting with the cap you can check yourself:

Can a loose gas cap cause P0455?

Yes. A cap left loose, not clicked, or with a seal gone hard or cracked leaves the loop open, and several bulletins name the cap or its seal.

Check it, but check it once. If tightening the cap fixed it, Nissan says not to replace the cap or any other EVAP part. Owners in the complaints who replaced a cap still saw the light come back.

The filler neck and fill pipe

The filler neck and fill pipe run from the cap down to the tank, and capless fillers have flaps inside that must close. Debris that holds a flap open, a pipe out of position or a disconnected vent hose at the filler leaves the loop open.

Some carmakers have extended the fill pipe warranty, and on some capless fillers the fix is a flap unit, not the whole pipe. If your car has a capless filler, ask about both before paying for a pipe.

A vapor line or hose

Rubber and plastic vapor lines join the tank, the canister and the purge valve, and one that splits, chafes or slips off its fitting is a large leak. Some are visible with the hood up. Others sit above the tank and need it lowered.

Carmakers have filed fixes for a split purge hose, a loose line under the hood and lines chafing near the tank. Some of those jobs mean lowering the tank, and some are a quick reconnection.

The vent valve and the canister

The vent valve closes the canister's fresh-air side so the loop can be tested, and a valve stuck open is a large leak. The purge valve lets fuel vapor into the engine to burn.

GM's own diagnostic tip for P0455 checks the vent valve, then the purge valve, which sets this code when it sticks closed. No parts are required for the procedure itself.

The canister can crack or clog too, and some carmakers have extended its warranty to 10 years or 120,000 miles, with other terms in salt-belt states. GM tells technicians not to replace a canister unless it fails the leak test or has taken in too much dirt, dust or water.

A cracked cap seal

How do you fix a P0455 code?

Work outward from the cheapest thing that can cause it, and let a smoke test find what you can't see. To fix a P0455 code, start at the gas cap, and the first three steps cost little or nothing:

1. Tighten the cap to the clicks printed on it. Check the rubber seal for cracks or hardening, refit it, and drive normally until the readiness monitor reads ready.
2. Read every code and run the VIN. A dealer checks bulletins and warranty extensions by VIN, the 17-character vehicle identification number, and our free VIN checker lists the recall campaigns for your car's model year.
3. Follow the vapor lines you can see. With the hood up, look for a hose off its fitting or split at a bend.
4. Ask for a smoke test. The shop's smoke machine pushes visible vapor into the sealed loop and shows where it escapes. Ask what it costs, as its own line on the estimate.
5. Replace only what the test found, then clear and drive. Clear the code and drive with the tank about half to just under three-quarters full until the car's self-check, its readiness monitor, reads ready.

If the VIN check finds nothing, the smoke test still decides. If the smoke test finds nothing, ask whether the leak shows only with a full tank or after the car has sat.

If the light stays on after a repair, give the test a few days to rerun before buying a second part. Owners in the federal complaints saw it return, and Ford found that purge valves returned on several of its recent models tested fully functional.

The cap check and the look at the vapor lines aren't tests, so a leak above the tank can get past them. A second new cap for a light that hasn't had time to clear is the cheapest wrong answer on this page, but it's still a wrong answer.

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How much does it cost to fix a P0455 code?

Often nothing, if the cap only needed tightening, and some carmakers pay for the fill pipe or the canister under an extended warranty. Run the VIN before you pay for a part.

Past the cap, a smoke test finds the leak, and independent shops charge a $100–$200 fee for one. A revised vent valve on a 2015 Silverado 1500 then runs $185–$342 at an independent shop, parts and labor, and a purge valve on a 2019 Honda Pilot $100–$160.

The vapor canister is the priciest part: with its purge valve on a 2014 Focus 5-door, it comes to $261–$545, parts and labor. A new gas cap is the small end of the bill, which is the whole reason to find the leak before buying.

The smoke test is billed first, because the shop has to find the leak before it fixes it. Ask for its result, the hours and the rate on the written quote.

Why is the light still on after a new gas cap?

Because the leak test has to run again and pass before the light goes out, and the car runs it only when its conditions are met. Fixing the leak doesn't turn the light off at once.

A stored or pending code can stop a monitor, one of the car's own self-tests, from finishing. So clear the code once the repair is done, then drive with the tank about half to just under three-quarters full.

Expect several days of mixed driving, not one trip, because the test runs only when its conditions are met. Clearing the code the day before an emissions test resets the monitors to "not ready", and a 2001 or newer car fails New York's inspection with more than one monitor in that state.

Will a P0455 code clear itself or fail an emissions test?

It can clear itself once the leak is fixed, and until then it can fail an emissions test. The light may go off after three drives in a row in which the leak test passes, and the stored code may be erased after 40 warm-ups without the fault.

If the car can tell the leak was a loose cap, the light may go off once it confirms the cap is fastened. A stored code can fail in states that read the computer, and so can a cleared one whose monitors still read "not ready".

Which codes come with P0455?

The code beside it narrows the search, so read every code stored with P0455 before anything is replaced:

• P0456 or P0442. The same leak test at smaller sizes. See P0456 and P0442.
• P0441. A purge flow fault as well. See P0441.
• P0446. The vent valve didn't respond, which can also leave the loop open. See P0446.

With P0446 or P0441 beside it, ask for the vent and purge valves to be checked too. GM's large-leak tip checks both after the connections.

Which cars get a P0455 code most?

Ford brands lead narrowly, with 9 Ford and Mercury complaints plus a Mazda Tribute against GM's 8. That's too few to rank makers, so the make alone tells you little.

For your car, the useful record is the bulletins. Some carmakers have extended the warranty on parts that cause it.

Common questions

Asked most often

What is the most common cause of a P0455 code?

Carmakers' bulletins name the cap, the filler neck and fill pipe, a vapor line off its fitting, and a vent valve stuck open. No document counts how often each one causes it, but the cap is the cheapest to check first.

Can you fix P0455 without replacing the EVAP canister?

Yes, because the canister is only one of the places the leak can be. On some Silverado and Sierra trucks, GM tells technicians not to replace it unless it fails the leak test or has taken in too much dirt, dust or water.

What is the difference between P0455 and P0456?

Size: P0455 is a large leak, the kind a loose cap or a hose off its fitting makes, and P0456 is a very small one of about 0.020 inch. The smaller the leak, the more a smoke test is needed to find it.

Prices are ranges compiled from September to November 2026 for the US market and vary by region, engine and shop rate. Prices from $10 up are rounded to the nearest dollar. Below $10 they're exact. This article is general information, not advice about your specific vehicle. See the disclaimer.