What does code P0455 mean?
Short answer
P0455 means the evaporative emissions (EVAP) system, which traps gasoline vapor from the fuel tank, found a large leak, roughly a hole 0.04 inch across or bigger. The most common cause is a loose, missing or worn gas cap, so check that first; after that the usual suspects are a stuck vent or purge valve, a cracked EVAP hose or a damaged charcoal canister.
Safety first. P0455 usually doesn't change how the car drives, and Edmunds says it may not cause immediate drivability problems. Escaping fuel vapor is still a fire and health concern, so if you smell gas strongly, don't keep driving it and get it checked. The code will also fail an emissions test in states that require one.
On this page
Step by step
- 1
Check the gas cap
Make sure the cap is there, seated and tightened until it clicks. Look at its rubber seal. If the cap or seal is cracked, torn or deformed, replace it. On capless fuel fillers, check that the flap closes fully.
- 2
Give the light a few drive cycles
If the cap was the problem, the check engine light should turn itself off after a few drive cycles once the system passes its leak test again. Clearing the code with a scan tool works too, but the code comes back if the leak is still there.
- 3
Look over what you can see
With the engine off and cool, check the rubber EVAP hoses you can reach and the fuel filler neck for cracks, rust or disconnected lines. A strong fuel smell near one spot points to the leak.
- 4
Have the system smoke tested
If the cap is good and nothing is visible, a shop pushes smoke into the EVAP system and watches where it comes out. That finds leaks in hoses, the filler neck, the canister and valves that you can't see by eye.
- 5
Test the vent and purge valves
A vent valve stuck open or a purge valve that won't seal can set P0455 with no actual hole. A shop checks that each valve clicks when powered and holds vacuum, and that the fuel tank pressure sensor reads correctly.
What the EVAP system does
Gasoline gives off vapor. Instead of venting it into the air, your car stores it in a charcoal canister and later pulls it into the engine to burn. The system is sealed, and the engine computer runs a leak test on it, usually by pulling a vacuum or watching pressure in the tank. RepairPal describes P0455 as the system finding it “cannot create enough vacuum pressure,” which is why a stuck-open valve can set it even without a real hole.
Common causes
| Part | What goes wrong |
|---|---|
| Gas cap | Loose, left off, or a worn or torn seal. The first thing to check. |
| Capless filler | Flap that sticks open (bulletin on 2021 Acura TLX) |
| Vent valve | Stuck open, sometimes from water getting in (common on Nissan, Infiniti, some GM trucks) |
| Purge valve | Stuck open (common on Hyundai, VW, Audi) |
| Hoses and lines | Cracked, split or disconnected EVAP hoses |
| Filler neck | Rusted or damaged |
| Charcoal canister | Cracked or damaged |
| Sensors | Faulty fuel tank pressure sensor or leak detection unit (less common) |
What you’ll notice
Usually only the check engine light. Some cars also show a “check fuel cap” message. You might smell fuel if the leak is big, and Samarins notes some GM trucks get hard to fill when the vent side is the problem.
When to see a pro
Checking and replacing the gas cap is a fine DIY job. Finding a leak beyond that needs a smoke machine and a scan tool that can command the valves, so most people should take it to a shop. Don’t let it ride for months: it will fail an emissions test where one is required, and a leak tends to get bigger.
Common follow-up questions
Can a loose gas cap really turn on the check engine light?
Yes. All three of our sources name a loose, missing or defective gas cap as a common cause, and Edmunds says mechanics check it first. The EVAP system checks that the fuel system is sealed, and an open cap is a big enough leak to set P0455.
How long after tightening the gas cap does the light go off?
Not right away. Samarins says the light should reset itself after a few drive cycles. The system has to rerun its leak test and pass before the computer turns the light off.
What's the difference between P0455, P0442 and P0456?
They're the same EVAP leak test with different leak sizes. P0455 is a large leak, P0442 is a small leak, and P0456 is a very small leak. Samarins notes P0455 often shows up together with P0456.
Is it safe to drive with P0455?
Usually the car runs normally, so a short drive to get it checked is typical. Edmunds says it may not cause immediate drivability issues but can cost fuel economy, and escaping vapor is a safety concern. If you smell strong fuel, stop and get it looked at.
Will P0455 fail an emissions test?
Yes, in states that test. Edmunds says ignoring it can lead to failing emissions testing that's required in many regions, and lists a failed test among the symptoms.
Are some cars known for P0455?
Yes. Samarins lists service bulletins for a sticking capless filler on the 2021 Acura TLX, water getting into the vent valve on 2007-2010 GM trucks, a stuck canister close valve on 2012-2017 Kia Rio, and a split purge hose on the 2015 Jeep Grand Cherokee and Dodge Durango. Purge valves are a common cause on Hyundai, VW and Audi, and vent valves on Nissan and Infiniti. Ask a dealer to check bulletins for your exact car.
Sources
- 1.Edmunds: Understanding error code P0455
- 2.Samarins: P0455 Evaporative Emission Control System Leak Detected (Large leak)
- 3.RepairPal: P0455 OBD-II Code, Evap System Gross Leak
General information only, not a diagnosis. Your owner’s manual comes first. How we write these