P0455 code: Evaporative Emission System Leak Detected (Large Leak)
P0455 means evaporative Emission System Leak Detected (Large Leak). The code says where to look, not what failed — the fix depends on which cause your car actually has.
What P0455 means
The evaporative emission (EVAP) system seals fuel-tank vapors and routes them to be burned. P0455 means the computer detected a LARGE leak — the system couldn't hold pressure or vacuum at all. The number-one cause is a gas cap left loose, worn out, or missing, which is also the cheapest thing in OBD to fix. Beyond that, a cracked or disconnected EVAP hose, or a vent valve stuck open, are the usual culprits. Because it's a large leak, it's often easier to find than the small-leak codes. It has no effect on how the car runs.
P0455 symptoms
- Check-engine light with no change in how the car drives
- Sometimes a noticeable fuel smell
- Frequently appears right after refueling
- Failed emissions test
What it costs to fix P0455
Typical range: $20–$400 · about ~0.2–1.5 hrs of labor
| If the cause is… | Part | Labor |
|---|---|---|
| Gas cap | $10–$35 | ~0–0.2 hrs |
| EVAP hose / line repair | $10–$80 | ~0.3–1 hrs |
| Vent valve | $30–$130 | ~0.3–1 hrs |
| Filler neck | $60–$250 | ~0.5–1.5 hrs |
Start with the gas cap — for a large leak it's the most common and cheapest cause. Hoses and the vent valve are still modest; a rusted filler neck is the priciest typical outcome.
The price swings on which cause it turns out to be — so confirm the cause before paying. Diagnose P0455 for my exact vehicle →
How to fix P0455
Easy — basic tools, most owners can do this
- Check that the gas cap is on and tight
A large EVAP leak is very often simply a cap left loose — or sitting on the roof of the car at the last gas station. Confirm it's present, seat it, and tighten until it clicks. If it was loose, expect the light to clear itself over the next few drives.
- Inspect the cap seal and filler neck
With the cap off, examine its gasket for cracks and the filler neck's sealing lip for rust or dents. A corroded neck can't seal even against a brand-new cap, and it's a known failure on older vehicles.
- Look for disconnected or split hoses
Unlike the small-leak codes, a large leak is often big enough to see: follow the EVAP hoses from the tank to the canister and up to the purge valve, checking for lines knocked off their fittings, split rubber, or damage from road debris. You may even hear hissing or smell fuel near the fault.
- Test whether the vent valve is stuck open
A vent valve that never closes means the system can't seal at all, which reads as a large leak. Apply 12 volts to the valve near the canister and confirm it clicks shut; replace it if it doesn't.
- Smoke-test only if the leak stays hidden
Most P0455 causes are findable by eye, which is what makes this the more forgiving of the leak codes. If yours isn't, a shop smoke test will show exactly where the vapor is pouring out.
DIY or shop? P0455 is among the most DIY-appropriate codes there is — the top cause is fixed by hand-tightening a cap, and because the leak is large, most other causes are visible on a careful crawl-around inspection. Vent valve testing needs only a test lead. Reserve the shop for the minority of cases where nothing shows up visually and a smoke machine is needed to trace it.
Tools for the DIY steps: Flashlight · OBD-II scan tool · Jack and jack stands or ramps · Jumper wires or a fused test lead · Replacement gas cap
Not sure which step applies to your car? Get the likely cause for your exact vehicle before buying anything for P0455.
Start a case with P0455 and your car. Redline weighs these causes against what your car shows, and names the check that would settle it before you buy parts.
Can I drive with P0455?
Redline can’t determine from a symptom or code alone whether your car is safe to drive.
P0455 on specific vehicles
The likely causes shift by model. We’ve written up the patterns we see most:
P0455: common questions
Can I drive with P0455?
Redline can't tell that from the code by itself. The main consequence of P0455 is failing an emissions test, so check the gas cap first and fix it at your convenience, ideally before inspection.
Will a new gas cap fix P0455?
Very often, yes — a large EVAP leak is most commonly a loose, worn, or missing gas cap. Tighten it until it clicks or replace a damaged one, then drive a few cycles; the light may clear by itself. If it returns, check the hoses and vent valve.
How much does it cost to fix P0455?
Frequently almost nothing — a gas cap is the cheapest OBD repair. Hoses or a vent valve are still modest. The priciest common cause is a corroded filler neck. A smoke test pinpoints a hidden leak.
What's the difference between P0455 and P0442?
P0455 is a LARGE EVAP leak (often a missing or loose gas cap, easier to find); P0442 is a SMALL leak (a tiny crack or seal that takes a smoke test to locate). Same system, different leak size.
Symptoms that trigger P0455
Drivers who get this code often notice one of these. Each has its own causes and cost guide:
Related trouble codes
Don’t have a scanner yet? A ~$25 Bluetooth adapter reads codes like P0455 from your phone. See our guide to the best OBD2 Bluetooth adapters. Run a repair shop? See Redline for shops.
Generic OBD-II reference. Manufacturer-specific behavior varies. Confirm with a scan tool and, for safety-related codes, a professional inspection. Cost ranges are reference ranges, not quotes.
Seeing P0455 on your car?
Every problem becomes a Case. Tell Redline what the car is doing: it shows what the evidence supports, what’s still missing, and what to check next, before you approve a repair.
“Inner pad ~1 mm. Outer pad 3 mm.”
Next: check the slide pins move freely before buying parts.