P0455 means the evaporative emissions (EVAP) system has detected a large leak. The EVAP system captures fuel vapors from the gas tank so they don't escape into the atmosphere. A large leak often points to a loose or missing gas cap.
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Can a loose gas cap cause P0455?
Yes — a loose, cracked, or missing gas cap is the #1 cause of P0455. Tighten the cap until it clicks, clear the code, and see if it returns. If it does, the leak is elsewhere in the EVAP system.
Is it safe to drive with a P0455 code?
Yes, P0455 rarely affects drivability. You may notice a slight fuel smell. However, you may fail an emissions test, so it should be fixed before inspection.
How do I find an EVAP leak?
A mechanic uses a smoke machine to pressurize the EVAP system and find the leak. Without that, checking the gas cap, visible hoses, and the purge valve are the best DIY starting points.