P0455: EVAP Large Leak — Causes and First Steps
Key Takeaway
P0455 means a large leak in the EVAP system. Despite the name, it's usually something simple.
What Is P0455?
"Large leak" sounds scary, but P0455 is often caused by a gas cap that's completely off or badly worn.
Common Causes
| Cause | Likelihood | Fix Cost |
|---|---|---|
| Gas cap missing or not closed | Very common | $0 – $15 |
| Gas cap seal completely failed | Common | $10 – $20 |
| EVAP canister vent valve stuck open | Moderate | $100 – $250 |
| Disconnected EVAP hose | Moderate | $50 – $100 |
| Cracked charcoal canister | Less common | $200 – $400 |
What to Check First
1. Is the gas cap on and tight?
2. Inspect the gas cap seal for visible cracks.
3. Try a new gas cap ($10) — cheapest test.
4. If code persists, get a smoke test.
ProHow Steer Helps
Steer identifies P0455, tells you it's almost always the gas cap, and guides you through confirmation steps.
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