Emissions

P0455 — EVAP System Large Leak Detected

Severity: low Safe to drive

What P0455 means

The EVAP system traps fuel vapor from the tank in a charcoal canister and later burns it in the engine. The engine computer regularly tests the system by applying vacuum or pressure and watching how well it holds. If it can't hold, as with a large leak, the PCM stores P0455 and turns on the check engine light.

Symptoms

  • Check engine light on
  • Fuel vapor smell around the vehicle
  • Light comes on soon after refueling
  • Failed emissions inspection
  • Slightly worse fuel economy (not always)

Possible causes

  1. Loose, missing or damaged gas cap
  2. Cracked or disconnected EVAP hose
  3. Faulty purge valve
  4. Faulty or stuck vent valve
  5. Damaged charcoal canister
  6. Damaged filler neck or fuel tank
  7. Leaking line connections

How to diagnose

  1. Read the code and freeze frame data, and note whether it appeared after refueling
  2. Inspect the gas cap for tightness, a worn seal and cracks
  3. Clear the code and see if it returns after a few drive cycles
  4. Inspect EVAP hoses and lines from the tank to the engine bay
  5. Read the fuel tank pressure sensor values with a scan tool
  6. Command the purge and vent valves and confirm they respond and seal
  7. Smoke-test the EVAP system to locate the leak
  8. Inspect the canister and filler neck

Common fixes

  • Tighten or replace the gas cap
  • Replace damaged EVAP hoses or lines
  • Replace the purge or vent valve
  • Replace the charcoal canister
  • Repair or replace the filler neck or tank

P0455 on different brands

Ford · manuals
On Ford, P0455:00 (no sub type) in the 2024-2025 gasoline OBD strategy means an EVAP large leak was detected; it describes the monitor condition, not a confirmed failed part.

Questions and answers

Can a gas cap cause P0455?

Yes, it is the most common cause. A loose, cracked or wrong cap can create a large leak. Tighten it until it clicks, clear the code and see if it returns after a few drives.

Is it OK to drive with P0455?

Usually yes, because it doesn't affect drivability. Still, fix it soon to stop vapor release and to pass an emissions test.

This is general information about the code. The meaning can differ between makes and models: a scan tool and the repair manual for your car will show the exact cause.