P0455: Evaporative Emission System Leak Detected (Large Leak)
A large leak has been detected in your evaporative emission (EVAP) system - the system that captures fuel vapors from your gas tank so they don't escape into the air. The most common cause is a loose gas cap.
Symptoms
- Check engine light
- Fuel smell near vehicle
- Failed emissions test
Causes (Ranked by Likelihood)
50 Most Common OBD2 Codes - Free Printable
Plain-English explanations for the codes mechanics charge $100+ to diagnose.
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DIY Fix Steps
⚠ Safety first: work on a cold engine, chock wheels, use jack stands - never rely on a floor jack alone.
Remove and firmly reinstall gas cap. It should click 3+ times. Clear the code and drive. If code doesn't return in 50 miles, cap was the culprit ($5-20 for new cap).
Trace the EVAP lines from fuel tank to charcoal canister to purge valve to intake manifold. Look for cracked, dry-rotted, or disconnected hoses.
Locate purge valve (usually on intake manifold or near charcoal canister). With engine off, blow into valve - if air passes freely, valve is stuck open (should be closed at rest). Replace if so ($15-50).
For hard-to-find leaks, a smoke machine test ($50-100 at shop) pressurizes the EVAP system and shows exactly where vapor is escaping.