P0455low severityGenerally driveableP0455 Code: Evaporative Emission System Leak Detected (Large Leak)
Written in plain English and reviewed by the eli5cars editorial team · Last reviewed June 2026
What it means in plain English
Same concept as P0442 — your fuel vapor system has a leak — but this time the leak is large enough that the ECM flagged it as a 'gross' leak. A large EVAP leak often means the gas cap is off or cracked, or a vapor hose has completely disconnected. It can also be a failing purge valve or a cracked charcoal canister. The car will run fine, but you're venting fuel vapors and will fail emissions.
Most likely causes — ranked
#1 Missing, loose, or damaged gas cap (most common trigger of a 'large' EVAP leak)
most likelyFix: Check that the gas cap is fully installed. A cap that is cross-threaded, cracked, or whose rubber seal is dried out will allow enough airflow to trigger P0455. Reinstall firmly (listen for clicks). If the seal is visibly damaged or the code returns after a few drive cycles, replace the gas cap — they're $10–$25 at any auto parts store.
#2 Disconnected or severely cracked EVAP vapor hose
likelyFix: A completely disconnected vapor hose creates exactly the large-leak signature that P0455 describes. Inspect the large-diameter hose running from the fuel tank area to the charcoal canister and from the canister to the purge valve. A hose that's popped off a fitting is obvious; a cracked hose may need a smoke test to locate.
#3 Failed EVAP vent control valve (vent solenoid) stuck open
possibleFix: The vent valve controls airflow into and out of the charcoal canister. When it fails open, the system can't seal itself during the self-test the ECM runs. Often located near or on the charcoal canister under the rear of the vehicle. Can be tested with a multimeter for proper resistance and function.
#4 Cracked or physically damaged charcoal canister
possibleFix: Road debris can crack a vapor canister, especially on low-riding vehicles. A cracked canister creates a large enough leak to set P0455. A smoke test locates it; replacement involves removing the canister from its mounting bracket under the vehicle.
Check engine light on? Get a free code scan
If your check engine light is on, most auto-parts stores (AutoZone, O'Reilly, Advance) will read the code for FREE — no purchase required, just walk in. Bring the code back here and look it up at eli5cars.com/obd2 for the plain-English explanation.
Note: a scan only helps when there's an active fault code. For purely mechanical symptoms (noises, vibrations, leaks), a scan may show nothing — the suspects listed above are your starting point.
Want to read the codes yourself?
First, the free option: AutoZone, O’Reilly, and Advance Auto Parts read your codes for free — no purchase needed. That’s the cheapest way to get the code to look up here. If you’d rather have your own so you can check anytime (and clear a code after a fix), the Veepeak OBDCheck BLE is an inexpensive, reliable plug-in reader that pairs with a free phone app and works on any car sold since 1996.
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Frequently asked questions
Can I drive with a P0455 code?
Yes — it's an emissions fault with no effect on engine operation or safety. You will fail an emissions test. Fix it when convenient, starting with the gas cap.
The gas cap seems fine. How do I find the large EVAP leak?
A smoke test at a shop is the cleanest way. They pressurize the EVAP system with visible smoke from the service port and watch for smoke escaping at the leak point. This test typically costs $75–$120 and takes 30–45 minutes. It's far better than replacing components by guess.
I smell fuel near my car. Is that related to P0455?
Possibly. A large EVAP leak means fuel vapors are escaping into the atmosphere instead of being captured. A noticeable fuel smell near your fuel filler or under the car can be related to the same disconnected hose or failed vent valve. If the fuel smell is very strong or you see fuel (liquid), that is a separate and more serious issue — see a shop immediately.
How is P0455 different from P0442?
P0442 = small EVAP leak (less than approximately 0.020-inch orifice equivalent). P0455 = large EVAP leak (more than approximately 0.080-inch equivalent). The ECM runs the same sealed-system self-test; P0455 means the system is leaking so badly it failed the test quickly and decisively rather than at the margin.