OBD-II trouble code
P0455: Evaporative Emission System — Large Leak Detected
The engine computer detected a large leak in the evaporative emission (EVAP) system. The most common cause is a loose, missing, or damaged gas cap. The car runs normally but will fail an emissions test until the leak is fixed.
Quick facts
- System
- Powertrain
- Category
- Emissions / EVAP
- Severity
- Low severity
- Drivable
- Usually safe to drive short-term
- Repair cost range
- $20 – $600
- DIY difficulty
- Beginner DIY
What does P0455 mean?
The evaporative emission (EVAP) system captures fuel vapors from the gas tank and routes them back into the engine to be burned, instead of releasing them into the atmosphere. The engine control module (ECM) periodically tests the system by sealing it and either pressurizing or applying vacuum, then watching for the seal to hold. A large leak — typically equivalent to a 0.040-inch or larger opening — is detected when the system cannot hold pressure at all.
P0455 is the "large leak" version of the EVAP code family. P0442 covers a small leak, P0457 specifically indicates a loose fuel cap, and P0440 is the general malfunction code on older vehicles.
The most common cause is a fuel cap that's loose, missing, or has a worn sealing gasket. After the cap, the next likely culprits are damaged EVAP hoses, a failed purge valve, or a failed vent valve. The fix is usually inexpensive and does not affect how the car drives — but the code prevents the vehicle from passing an OBD-II emissions inspection.
Common causes
- Loose, missing, or wrong gas cap (the most common cause by a wide margin)
- Gas cap with worn or damaged sealing gasket
- Cracked or disconnected EVAP hose between the fuel tank and the engine
- Failed purge valve stuck open
- Failed vent valve stuck open or unable to close
- Damaged or cracked charcoal canister
- Damaged fuel filler neck or filler tube
Symptoms
- Check engine light is on
- Occasional faint fuel odor near the rear of the vehicle
- Fuel level may drop slightly faster than normal in extreme cases
- Vehicle fails an OBD-II emissions inspection
- No driveability symptoms
Diagnostic steps
- 1.Check the gas cap first. Inspect the rubber sealing gasket for cracks, dirt, or deformation. Tighten until it clicks. Drive 3 to 5 full drive cycles and rescan.
- 2.Visually inspect EVAP hoses from the fuel tank to the engine bay. Look for cracks, loose clamps, or chewed lines (rodent damage is common).
- 3.Smoke-test the EVAP system. Most independent shops have a smoke machine that pressurizes the system with theatrical smoke and reveals the leak source.
- 4.Use a scan tool to functionally test the purge valve and vent valve. They should hold pressure when commanded closed.
- 5.If the leak is in a hard-to-reach component like the charcoal canister or filler neck, plan for a shop visit — those repairs are difficult to confirm without a smoke machine.
Repair cost
$20 – $600
A new gas cap costs $15 to $40 and resolves a large share of P0455 cases. EVAP hose or valve replacement runs $100 to $400 including labor. Smoke testing typically adds $50 to $150 to a shop visit. Charcoal canister replacement on the upper end can reach $400 to $700 on some vehicles.
Estimate your repair
Run the numbers for your vehicle
Open the Repair Cost Estimator with evap system repair preselected. Adjust labor rate and vehicle category to fit your situation.
Related repairs
DIY vs shop
This is a beginner-friendly repair. Common hand tools, a free afternoon, and a willingness to follow a procedure are usually enough. The risk of causing a bigger problem is low if you read up on your specific vehicle first.