Car & driving · Free
P0455: large leak in the fuel vapor system (EVAP)
P0455 means the car could not hold pressure or vacuum in its fuel vapor system during its leak test. A missing or loose fuel cap is the classic reason, followed by a split hose or a valve that stays open. It does not change how the car drives.
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- Runs on your device
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Check your car for P0455
Runs on your device
Connect your OBD2 adapter
- Plug the adapter into the OBD2 port – usually under the steering wheel, near the pedals.
- Switch the ignition on, or start the engine.
- Bluetooth adapter? Turn Bluetooth on. Nothing else to set up.
This browser cannot talk to OBD adapters. Use Chrome or Edge on Android, Windows or Mac – on iPhone, the free Bluefy browser works with Bluetooth LE adapters. The demo car works everywhere.
Classic Bluetooth adapter (PIN 1234)? Pair it in your system settings first, then choose USB or paired Bluetooth – on a computer or in Chrome 138+ on Android. Wi-Fi adapters cannot work in a browser.
Your car data stays on your device. The page talks to the adapter directly; codes, VIN and values are never uploaded.
Never use it while you drive. Set things up before you set off, or let a passenger handle the phone. Standard OBD2 reads engine and emissions data; ABS, airbag and coding need workshop equipment.
What P0455 means
Petrol gives off vapor, and the EVAP system catches it in a charcoal canister instead of letting it into the air. While the engine runs, a purge valve lets the engine draw those vapors in and burn them. To make sure the system is tight, the car regularly seals it, creates a slight vacuum or pressure and checks whether it holds.
P0455 means the system leaked so much that the test failed straight away: roughly a missing cap or a disconnected hose. Smaller leaks set P0442 or P0456. Leak tests like this are required in the US but not in the EU, so many European models never set this code.
Symptoms of P0455
- Usually no change in driving at all.
- A smell of petrol around the car, especially after refuelling or on hot days.
- A Check fuel cap message on some cars.
- A failed emissions test where the EVAP self-test is checked.
Causes of P0455, cheapest first
Work down the list in order: the first checks cost little or nothing, the last ones are jobs for a workshop.
A missing, loose or worn fuel cap
Check that the cap is there and turn it until it clicks. Look at the rubber seal for cracks; a new cap is the cheapest fix of all.
The filler neck
Rust or damage around the filler neck stops the cap from sealing. Inspect the rim where the cap sits.
A disconnected or split vapor hose
The hoses to the canister and the purge valve run near hot or moving parts. Follow them from the tank to the engine and look for cracks, loose clips and chafing.
A purge or vent valve that stays open
The purge valve near the engine and the vent valve near the canister must close for the test. A valve stuck open makes the system look like it has a big leak. A workshop can test both.
A cracked charcoal canister
Stone chips or age can crack the canister housing. A smoke test, which fills the system with visible smoke, shows leaks that are hard to see.
Can you drive with P0455?
Safe to drive. P0455 is an emissions fault: the engine runs exactly as before. Fix it before an inspection, and sooner if you smell fuel inside or around the car; then check the hoses and the filler area for a real fuel leak.
Check P0455 with OBD Studio
Connect your adapter above, or try the demo car, then:
- Tighten or replace the fuel cap, then clear the code in Fault codes.
- Drive as usual for a few days. Most cars run the leak test only under certain conditions, often after standing for several hours and with the tank between a quarter and three quarters full.
- Watch the Fuel vapour system (EVAP) monitor in Inspection: once it shows Complete without the code returning, the system is tight.
- On cars with CAN, Read self-tests in Inspection lists the EVAP leak test result when the car reports it.
More fault code guides
Each of these codes has its own page with causes ranked by cost and the checks that go with them.
- P0420Catalyst efficiency below threshold
- P0171System too lean
- P0300Random or multiple misfire
- P0442EVAP system small leak
- P0128Engine warms up too slowly
- P0172System too rich
- P0401EGR flow too low
- P0101Air flow sensor implausible
- P0135Front O2 sensor heater
- P0016Crankshaft and camshaft out of step
- P0011Intake camshaft timing over-advanced
- P0141Rear O2 sensor heater
- P0113Intake air temperature sensor high
- P0457Fuel cap loose or missing
- P0299Turbo underboost
- P0700Transmission control system fault
- P0087Fuel rail pressure too low
- P0562System voltage low
- U0100Lost communication with engine computer
More OBD Studio pages
Frequently asked questions
Is P0455 always the fuel cap?
No, but it is the first thing to check because it costs almost nothing. If a tight, intact cap does not help, the next suspects are a split hose and a purge or vent valve that does not close.
How long until P0455 clears after a fix?
You can clear the code yourself right after the repair, or wait: the light goes out once the leak test has passed on several drives. Because the car runs this test only under certain conditions, that can take a few days.
What is the difference between P0455 and P0442?
Both are leaks in the same system. P0455 is a large leak, such as a missing cap or a disconnected hose; P0442 is a small one, such as a worn seal or a hairline crack, and is usually harder to find.
Can I read P0455 without going to a workshop?
Yes. With any ELM327-compatible Bluetooth LE or USB adapter, OBD Studio on this page reads P0455 and every other stored code for free, shows the freeze frame and clears the code after the repair. Nothing to install, no account.
