P0455: EVAP System Leak Detected (Large Leak)

P0455 quick answer

P0455 means the EVAP system found a large fuel-vapor leak. Most of the time the gas cap is missing, loose or has a failed seal; the next suspects are a disconnected or split EVAP hose and a stuck-open vent valve. It is safe to drive but will fail an emissions test.

Severity: Low
Can I drive? Yes, and for longer than most check-engine codes. Even the "large leak" P0455 only affects how well the car contains fuel vapor - it does not change engine performance, power, or safety.
Typical fix: $20 - $600

Also written as PO455 or P455.

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What P0455 means

P0455 means the EVAP system has detected a large leak - a bigger vapor leak than P0442. The most frequent cause is a gas cap that was left off, not clicked tight, or has failed, but a disconnected or split hose and a stuck-open vent valve are also common. The car drives normally, but the code needs fixing to pass emissions and to contain fuel vapors.

Symptoms of P0455

Check-engine light on
Noticeable fuel odor in some cases
No change in how the car drives
Fails emissions test

Is it safe to drive with P0455?

Yes, and for longer than most check-engine codes. Even the "large leak" P0455 only affects how well the car contains fuel vapor - it does not change engine performance, power, or safety. Drive normally. Fix it before your next emissions test, because that is the only thing it will actually fail you on, and check the gas cap first, since that resolves most P0455 cases for free.

Common causes of P0455

Gas cap left loose, off, or failed
Disconnected or split EVAP hose
Stuck-open or failed vent valve
Failed purge valve
Damaged charcoal canister

Listed roughly most-likely first. Confirm with a scan tool and the freeze-frame data before replacing parts.

What the P0455 fix costs

Fix	DIY parts	At a shop
Replace the gas cap	$10 - $25	$20 - $40
Replace the vent or purge valve	$20 - $80	$100 - $300
Reconnect or replace an EVAP hose	$10 - $60	$80 - $250
Replace the charcoal canister assembly	$80 - $300	$250 - $600

Ranges are rounded and for the US market only - actual price depends on region, shop labor rates, and the exact make and model.

Parts that commonly fix P0455

Fuel cap - Cause #1: a worn, cracked or loose cap seal. Caps are not universal - match yours to the filler neck (capless fillers have no cap)
EVAP canister vent valve - A vent valve stuck open reads as a leak - especially on trucks, where it sits near the canister
EVAP purge valve - A purge valve that seeps lets the system lose its test vacuum
EVAP smoke leak tester - Finds a pinhole EVAP or vacuum leak that a visual check misses - cheaper than a shop smoke test if you will use it twice
OBD-II scanner - Reads and clears codes, and shows live data so you fix the cause rather than the symptom

These open an Amazon search - add your year, make and model, because most of these parts are fitment-specific.

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What P0455 actually means

P0455 means the evaporative emissions system failed a leak test at the large-leak threshold - the PCM pressurized or pulled vacuum on the fuel tank and the pressure went nowhere. EVAP exists to stop fuel vapor escaping to atmosphere, so a large leak is an emissions failure rather than a drivability problem. Your car will run normally. The single most common cause is genuinely the gas cap, which is why every mechanic checks it first and why you should too before spending a dollar.

How to diagnose P0455 step by step

Step 1: Remove, inspect, and properly reseat the gas cap Pull the cap and look at the rubber O-ring seal. Cracked, flattened, hardened, or missing means replace it. Then reseat until it clicks at least three times - a cap that is on but not clicked is a large leak by definition. Clear the code and drive several days before concluding anything.
Step 2: Check whether the cap is aftermarket Cheap universal gas caps are a well-known P0455 cause. They thread on and feel tight while sealing poorly against the specific filler neck profile. If someone fitted a generic cap, put an OEM one on before diagnosing further.
Step 3: Inspect EVAP lines from tank to canister to purge valve Follow the hard lines and rubber sections along the frame rail. You are looking for cracked, brittle, or disconnected hose - and for rodent damage, which is extremely common on vehicles that sit. A visibly chewed line is your leak.
Step 4: Test the purge valve for a stuck-open condition With the engine off the purge valve should hold vacuum and not pass air. Apply vacuum with a hand pump - if it bleeds down, the valve is stuck open and the system can never seal, which reads exactly like a large leak.
Step 5: Check the canister vent valve, especially on trucks and SUVs The vent valve lives underneath, exposed to road salt and spray, and corrodes until it cannot close. On pickups and SUVs this is the second most common P0455 cause after the cap.
Step 6: Smoke test the system if the leak is still hiding Introduce smoke into the EVAP service port and watch where it escapes. This is the only method that finds a cracked canister or a pinholed tank seam quickly, and it turns an afternoon of guessing into a ten-minute answer. Many auto parts chains rent the machine.

The most common P0455 misdiagnosis

Do not replace the charcoal canister just because it is the biggest EVAP component. It is expensive and rarely the failure. Work the cheap causes in order - cap, hose, purge valve, vent valve - and the canister almost never comes up.

Tools you need for P0455

EVAP smoke machine - The one tool that makes an invisible leak visible. Rent it rather than buy it for a single repair.
Hand vacuum pump - Tests the purge and vent valves for seal without removing them from the car.
Scanner with EVAP bidirectional control - Lets you command the valves closed and watch the fuel tank pressure sensor respond.
Inspection mirror and light - Most of the EVAP system is above the tank and behind the rear axle where you cannot see directly.

Parts you may need for P0455

OEM-spec gas cap - The cheapest possible fix and the statistically most likely one. Start here.
EVAP purge valve solenoid - If it failed the vacuum hold test in step 4.
Canister vent valve - The usual culprit on rust-belt trucks and SUVs.
EVAP hose - For replacing a cracked or rodent-chewed section. Use fuel-vapor rated line, never generic vacuum hose.

P0455: DIY or pay a shop?

Difficulty: Easy to Moderate. Time: 0.25 - 3 hours. DIY parts: $15 - $250. Shop total: $120 - $600.

If it is the gas cap, this is a fifteen-dollar fix you should absolutely do yourself. Beyond that, the honest tradeoff is diagnostic equipment - a shop with a smoke machine finds the leak in minutes and often charges about an hour of labor to do it. Paying for the diagnosis and doing the repair yourself is a smart split on this code.

How to stop P0455 coming back

Stop topping off the tank after the pump clicks. Forcing extra fuel past the first shutoff pushes liquid gasoline into the charcoal canister, which is designed for vapor only. A saturated canister causes EVAP faults and eventually needs replacing - a self-inflicted several-hundred-dollar repair. Log your fuel-ups and services in ServiceSage and you build the maintenance record that keeps small EVAP faults from turning into emissions-test failures at the worst possible time. Track this maintenance free.

P0455 by make

P0455 on Chevrolet vehicles

P0455 is one of the most-searched Chevy codes for a reason: on Silverado and Sierra trucks the canister vent valve sits near the spare tire, exposed to road grit, and sticking open is routine. On the Cruze and Equinox the purge valve is the usual culprit. Check the gas cap first, then test the vent solenoid before buying parts. Chevrolet maintenance schedule

P0455 on Ford vehicles

On F-150s the usual suspects after the gas cap are the canister vent solenoid and, on rust-belt trucks, a corroded fuel filler neck that no longer seals against the cap. A smoke test finds a filler-neck leak in minutes. Ford maintenance schedule

P0455 on Toyota vehicles

Toyota EVAP systems are reliable, but when a Corolla, Camry, or Tacoma sets P0455 beyond a loose cap, the charcoal canister assembly (which includes the vent valve on many models) is the common repair - pricier than average at $400-$600 installed. Toyota maintenance schedule

P0455 on Honda vehicles

Civics and CR-Vs most often trace P0455 to the purge valve on top of the engine - a $30-$60 part and a 15-minute DIY. Confirm it holds vacuum before replacing anything else. Honda maintenance schedule

P0455 FAQ

How much does it cost to fix P0455?

Typical US independent-shop repair cost for P0455 runs about $20 - $600, depending on the root cause. Common fixes: Replace the gas cap (about $20 - $40 at a shop); Replace the vent or purge valve (about $100 - $300 at a shop); Reconnect or replace an EVAP hose (about $80 - $250 at a shop); Replace the charcoal canister assembly (about $250 - $600 at a shop).

Can a loose gas cap cause P0455?

Yes - a loose, cracked, or worn gas cap is the single most common cause of P0455. Before assuming a bigger EVAP leak, make sure the cap clicks fully tight, or just replace it since caps are cheap, then clear the code and see if it returns. If it does, the vent valve, purge valve, and hoses are the next things to check.

Will P0455 clear itself?

Often, yes. If the leak was just a loose or worn gas cap, tightening or replacing it and driving through a few complete drive cycles (a full cold start followed by normal driving) usually lets the EVAP monitor pass on its own and the light goes out without a scan tool. If it has not cleared after several drive cycles, the leak is elsewhere and needs to be found.

Is PO455 the same code as P0455?

Yes. OBD-II codes use a zero after the letter, but it is easy to read or type it as the letter O - PO455, P455 and P0455 all refer to the same large EVAP leak code.

What is the difference between P0455 and P0456?

Both are EVAP leak codes; they differ in the size of the leak the self-test found. P0455 is a large leak - typically a gas cap that is off, loose or not sealing, or a hose that has come off - while P0456 is a very small, pinhole-size leak. A large leak is usually easier to find by eye; a very small one normally needs a smoke test.