Applicable Systems
OBD-II
Symptoms
EVAP system large leak detected; significant fuel vapor leak; gas cap missing or major hose disconnect.
Possible Causes
- Gas cap missing or not installed
- EVAP supply hose disconnected
- Charcoal canister large crack
- Purge valve stuck wide open
Troubleshooting Steps
- Step 1: Check if gas cap is installed and tight
Cap installed and clicks tight - Step 2: Inspect EVAP supply hose connections
All hoses connected - Step 3: Check charcoal canister for visible damage
Canister intact - Step 4: Test purge valve for stuck open
Valve closes when not commanded - Step 5: Perform smoke test to locate large leak
Leak located and repaired
How to Reset
Clear with OBD-II scanner after repair; verify with EVAP self-test.
Common Replacement Parts
- Gas Cap (OEM spec)
- EVAP Purge Valve
Frequently Asked Questions
- Q: What causes P0455 most commonly?
Missing gas cap (forgot to put it back after refueling) or loose gas cap. Check this first before more complex diagnosis.
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Source: SAE J2012 standard DTC list + OBD-II portal
Category: OBD-II
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