P0455 EVAP Leak — Usually Just Your Gas Cap

Common causes

• loose, missing, or worn gas cap (60%+ of P0455 cases)
• cracked EVAP hose under the vehicle
• failing purge or vent solenoid valve
• fuel tank seam leak (rare, but expensive)

How a mechanic diagnoses it

1. tighten the gas cap until it clicks 3+ times, drive 50 miles, see if code clears
2. visual + smoke test of all EVAP hoses under the chassis
3. actuator test on the purge and vent solenoids via scanner
4. pressure-decay test on the tank itself

Typical fix cost

$0–$250 — most common fix: tighten or replace gas cap ($0–$25 part). Actual cost varies by vehicle year/make and local labor rates; Fixo's AI estimate adjusts for both.