What Does P0455 Mean?
The EVAP system has detected a large leak during its self-test. This means the system was unable to build or maintain any meaningful vacuum, indicating a significant opening in the fuel vapor containment system. The most common cause is a loose, missing, or damaged gas cap. The driver will see a check engine light and may notice a fuel odor near the vehicle.
Common Causes
40%
Loose, missing, or damaged gas cap (cracked, worn O-ring, or not tightened properly)
25%
Disconnected, cracked, or deteriorated EVAP hose
15%
Failed or stuck-open purge valve or vent valve
10%
Cracked or leaking charcoal canister
10%
Fuel tank leak (rust hole, cracked seam, or damaged fuel sender gasket)
Diagnostic Steps
1
Start with the simplest fix: remove the gas cap, inspect the O-ring seal for cracks or deformation, reinstall firmly until it clicks, clear the code, and drive through one complete EVAP monitor cycle.
2
If the code returns, perform an EVAP smoke test by introducing low-pressure smoke into the EVAP system through the service port. A large leak will produce visible smoke at the leak location.
3
Visually inspect all EVAP hoses and connections from the fuel tank to the charcoal canister to the purge valve. Check for disconnected hoses, cracked fittings, and deteriorated rubber.
4
Check the charcoal canister for cracks, especially if the vehicle has been in an underbody impact or has been exposed to fuel flooding of the canister.
5
If no external leaks are found, inspect the fuel tank seams, fuel sender gasket/O-ring, and filler neck connection for signs of seepage.
Estimated Repair Cost
$15 - $400
Parts + labor, varies by vehicle and location
The EVAP system has detected a large leak during its self-test. This means the system was unable to build or maintain any meaningful vacuum, indicating a significant opening in the fuel vapor containment system. The most common cause is a loose, missing, or damaged gas cap. The driver will see a che...
The most common cause of P0455 (Evaporative Emission Control System Pressure Sensor Intermittent) is: Loose, missing, or damaged gas cap (cracked, worn O-ring, or not tightened properly)
Typical repair costs for P0455 range from $15 to $400, depending on the vehicle, location, and whether you do it yourself or go to a shop.
Safe to drive, but a large EVAP leak means fuel vapors are escaping to the atmosphere. While not an immediate safety hazard, fuel vapors are flammable and the vehicle will fail emissions testing. If a strong fuel odor is present, repair promptly.
Start by connecting an OBD2 scanner to read the code and any freeze frame data. Then follow the diagnostic steps specific to P0455 to identify the root cause.
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Quick Info
Category
Powertrain
System
EVAP / Emissions System
Difficulty
Type
Generic (SAE)
Recommended Tools
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