P0455 Code: Large EVAP Leak Cost, and the Cap Comes First

OilAndMiles.com - A P0455 code is an OBD-II code, and it means one thing: the fuel vapor system was pressure tested, and it leaked too much to pass. Not a misfire, not the engine. A sealed loop of hoses, a plastic canister and two valves that failed to hold.

That's worth knowing before a shop starts, because it rules out most of what an owner fears. The car still drives, and nothing is wearing out while you decide.

What it won't do is pass an emissions test, and while the hole is there the code comes back every time the monitor actually runs. Every code on this page reads the same way once you know the format, and what each character in an OBD-II code means takes two minutes to learn.

The car warns you about this code on the part itself

What does a P0455 code mean?

It means an evaporative emission system leak, and a large one. The system is the sealed loop that stops fuel vapor reaching the air, and it failed a pressure test by a wide margin.

The car runs that test on its own, usually after a drive, and stores P0455 when the loss is large rather than small. A scan tool will call it a DTC, a diagnostic trouble code, which is the same thing under the name the trade uses.

The system is a loop and it has to hold. Fuel tank, filler neck, cap, a charcoal canister that stores the vapor, a purge valve that lets the engine draw it in, and a vent valve that opens the loop to the atmosphere when it needs to breathe. Any of those can be the hole.

What is the most common cause of a P0455 code?

The fuel tank cap, and the car tells you so before the code ever appears. The cap in the photograph above is printed with a warning that a loose one will turn the light on, which makes the manufacturer the most direct source there is for this claim.

It's also where the published advice goes wrong. Google's own AI summary for this code, quoting a smoke machine seller, says to tighten the cap until you hear two to three sharp clicks.

The cap in the photograph says one. Manufacturers set that number, not the internet, and the only place it is written for your car is the cap and the owner's manual.

After the cap, in the order a leak this size usually appears: a vapor hose pulled off or split, the filler neck where it meets the tank, a vent valve stuck open, and the canister itself.

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One cause is entirely in your hands: topping off after the pump clicks off. The canister is built to hold vapor, not liquid, and the fuel you force in past that click has nowhere to go but into it. Consumer Reports makes the same point.

A canister soaked that way is the dearest part in the table below. It's also the only cause on this page you fix by not doing something.

Can you drive with a P0455 code?

Yes, and nothing is being damaged while you do. A large EVAP leak lets fuel vapor escape, which is an emissions fault rather than a mechanical one, and the engine neither loses power nor wears faster for it.

Two things it does cost you. It fails an emissions test in any state that runs one, and it keeps a fault stored that would otherwise be the light you notice when something worse arrives. A stored code hides the next one.

The exception is a fuel smell. A large leak that you can smell is fuel in liquid or vapor form where it shouldn't be, and that's a stop-and-look, not a wait-and-see.

How much does it cost to fix a P0455 code?

Between $2.76 and $536 for the part, depending which one it is. The cap is the cheap end and the canister the dear one, and the gap between them is the whole reason to look before buying:

The row that matters most is the first one. A cap at the counter is $2.76 to $43 with a brand and a part number you can type in yourself. A shop bills about $108 for the same piece before labor.

That's not a trick: a garage carries stock, warrants the work and often fits the maker's own part. It's worth knowing before you read a quote.

The Silverado leads that table because Chevrolet owners search this code more than any other brand's owners do, by roughly six to one over Toyota. If you arrived here typing P0455 code Chevy, the first row is yours.

One number in the table isn't where the published estimates put it. A vapor canister for the 4Runner runs $255 to $536, above the $400 ceiling the widely quoted cost tables use, and a Toyota owner working from those tables will underestimate this repair by a hundred dollars or more.

Why is a large leak easier to find than a small one?

Because the hole is bigger than the one the regulation makes your car detect at the small end. The federal rule sets that threshold at 0.020 inches, about the width of a pencil lead, which is why a P0456 code can take a smoke machine and a patient afternoon to chase.

P0455 is the other end of the same test. A leak this size is often a hose off its stub, a cap that never clicked, or a filler neck rusted through, and those can be found by looking. That's the good news buried in a code that sounds worse than the small one.

Why do P0441 and P0455 show up together on a Toyota?

Because they are two halves of one failure. P0455 says the loop leaked; P0441 says the purge flow was wrong at the moment it was measured. A loop that can't hold pressure will also fail to move vapor the way the computer expected, so one fault sets both codes.

The vent valve is on the cost list below because it can stick open, which is a leak. If it stops answering the computer altogether that is a different accusation and a different code, P0446, where checking the cap first is the wrong move.

Toyota owners search for the pair more than anyone else, and the cause named most often in those searches is an aftermarket cap. A cap that seals well enough to stop fuel escaping can still fail the pressure test, because the test is stricter than the seal. That's worth ruling out first on any car where the cap has been replaced with a non-original one.

Can you fix an EVAP leak yourself?

The cap, yes. Tighten it to the number of clicks printed on it, drive for a day or two, and see whether the light goes out on its own. If the seal is cracked or gone hard, a new one is under $43 for every car in the table above.

The hoses, often. A vapor line pulled off its stub or split at a bend is visible with the hood up and the car on the ground, and pushing it back on costs nothing.

Past that, no, and not because of skill. The leak that is left is somewhere you can't see, and finding it means pumping smoke into a sealed system and watching where it escapes. We don't publish a price for that test, because the figures circulating for it aren't attached to a source we could read.

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

Because the test that turns it off is one of the slowest the car runs, and it won't run at all while the old code is still stored. Fixing the leak and passing the retest are two different days.

So clear the code once the new cap is on. New York state's inspection program, which follows EPA guidance, says a stored or even pending fault can stop a monitor finishing. Leaving the code in memory is itself part of what keeps the light lit.

Then drive it, with the tank between a quarter and three-quarters full. We can't give you one number here, because the published ones disagree: New York says 35% to 85% on one page and 26% to 74% on another, and Ford asks for half to three-quarters. A quarter to three-quarters sits inside all of them.

Expect days of mixed driving, not one trip. Part of Chrysler's version of the test doesn't even begin until the car has stood for eight hours.

It's also why clearing the code the day before an emissions test fails you as surely as the light would. Clearing resets every monitor to not ready, and a 2001 or newer car fails New York's inspection with more than one monitor left in that state.

How do you fix a P0455 code?

Work outward from the cheapest thing that can cause it. 4 steps below:

1. Tighten the cap to the number of clicks printed on it. Not two or three because an article said so: the number is on the cap or in the manual, and on the one photographed above it is one. Then drive for a day or two and see whether the light clears itself. A lamp that goes out isn't proof on its own, because the monitor may simply never have run.
2. Look at the cap seal in daylight. A rubber ring that has gone hard, cracked or flat will pass a glance and fail a pressure test. A new cap is under $43 for every car in the table above, and it's the only part on this page you can buy on a guess without feeling foolish.
3. Follow the vapor lines with the hood up. You're looking for a hose off its stub or split at a bend, which is what a leak this size usually is. This costs nothing and rules out the second most common cause.
4. Ask for a smoke test, and ask what it found. If the cap and the visible hoses are sound, the leak is at the tank end and it needs smoke to locate. A shop that names a part without running one is guessing, and the part it names is the one in the dearest row above.

What none of these steps does is clear the code for you. Clearing it before the repair wipes the freeze frame the shop would have used, and it resets the emissions monitors, which can fail an inspection for days afterwards.

Common questions

Asked most often

What is the most common cause of a P0455 code?

The fuel tank cap, and the car says so on the part itself: many caps are printed with a warning that a loose one turns the check engine light on. Tighten it to the number of clicks printed there, not to a number from an article.

How much does it cost to fix a P0455 code?

Between $2.76 and $536 for the part, depending which one leaked. A cap is the cheap end and a vapor canister the dear one. RepairPal puts a cap job at $133 to $144 fitted and a canister at $547 to $633.

Can I drive with a P0455 code?

Yes. A large evaporative leak doesn't affect how the car runs, drives or stops. It fails an emissions test in any state that runs one, and it hides the next code that arrives. A fuel smell is the exception and is worth stopping for.

Can a loose gas cap cause a check engine light?

Yes, and it's the most common way this code appears. The cap seals the system the car pressure tests, so a cap that never clicked home leaves a hole the test finds.

Why do P0441 and P0455 show up together?

They're two halves of one failure. P0455 says the loop leaked and P0441 says the purge flow was wrong when it was measured, and a loop that can't hold pressure will do both. Toyota owners report the pair most often, frequently after an aftermarket cap.

Is P0455 a permanent code?

No. It clears once the leak is fixed and the car has run its own test again, which takes a drive or two. Clearing it yourself before the repair only wipes the freeze frame the shop would have used.

What is the difference between P0455, P0442 and P0456?

Size, not system. One test read at three thresholds: P0455 is the large leak, P0442 the small one, and P0456 the very small leak at around 0.020 inches, about the width of a pencil lead.

What is an EVAP leak detection pump, and does my car have one?

A small pump that pressurizes the sealed system so the car can watch the pressure fall. Which way your car tests is the maker's choice: Ford and GM pull a vacuum, so their cars have no pump. Chrysler used a pump from 1996, then natural vacuum detection, then the sealed monitor a modern Jeep or Ram still uses.

Is the second character in P0455 a zero or a letter?

A zero. Only the first character is a letter and the four after it are digits. A capital O and a zero look almost identical on a scan tool screen, so PO455 gets typed into parts catalogs every day, and the search comes back empty rather than correcting the slip.

Prices are US averages compiled in September 2026 and vary by region, engine and shop rate. Prices from $10 up are rounded to the nearest dollar, so $14.13 reads as $14 and $14.52 as $15. Below $10 they're exact. This article is general information, not advice about your specific vehicle, see the disclaimer.