Emission controls · Powertrain · generic (SAE-defined)
P0455: Evaporative Emission System Leak Detected (Large Leak)
P0455 means the engine computer found a large leak, or a complete lack of sealing, in the evaporative emission (EVAP) system that traps fuel vapor from the tank.
Standard title per SAE J2012 / ISO 15031-6 · Updated 2026-11-07 · By CarWhere Research
How P0455 sets
When conditions are right, usually after a cold soak with the fuel level in a set range, the powertrain control module (PCM) closes the canister vent valve and pulls a vacuum on the system through the purge valve, or pressurizes it with a leak detection pump. If the system cannot build the expected vacuum or pressure at all, or it collapses almost immediately, the PCM concludes there is a gross leak and sets P0455. Exact test procedures and limits are manufacturer-specific.
Common causes of P0455
Roughly most likely first; the actual cause depends on the vehicle and needs testing to confirm.
- Fuel cap missing, left loose, or not sealing
- Disconnected or split EVAP hose
- Purge valve stuck closed so no vacuum reaches the system during the test
- Vent valve stuck open so the system cannot seal
- Cracked charcoal canister
- Rusted-through or damaged fuel filler neck
- Leaking fuel pump module seal or tank fitting
P0455 symptoms
- Check engine light on
- Noticeable fuel vapor smell, especially near the rear of the vehicle
- Some vehicles display a check fuel cap message
- No drivability change in most cases
- Failed emissions inspection
How P0455 is diagnosed
- Confirm the fuel cap is present, the correct part, and clicks fully tight; inspect the seal and filler neck lip
- Scan for other EVAP codes, especially purge or vent circuit codes, and fix those first
- Inspect EVAP hoses from the tank to the canister and from the canister to the purge valve for disconnections or splits
- Command the vent valve closed and verify it seals; command the purge valve and confirm it opens
- Perform a smoke test of the EVAP system to pinpoint the leak
- Inspect the filler neck, canister, and tank-top seals if the leak is not found elsewhere
- After repair, allow the EVAP monitor to run or use a scan tool to run the EVAP self-test
Typical fixes for P0455
- Install or replace the fuel cap with a correct-fit cap
- Reconnect or replace damaged EVAP hoses
- Replace a stuck-open vent valve or stuck-closed purge valve
- Replace a cracked canister or rusted filler neck
- Reseal the fuel pump module or tank fittings
Replace parts only after testing confirms the cause — a code names the circuit or condition that failed a check, not necessarily the faulty part. We don’t publish per-repair prices; for what households actually spend on upkeep, see car repair costs.
Manufacturer notes
Seen across most makes. Vehicles with a natural vacuum or pump-based leak test may report the same condition differently; check factory service information.
Related codes & warning lights
P0455 FAQ
What does code P0455 mean?
P0455 means the engine computer found a large leak, or a complete lack of sealing, in the evaporative emission (EVAP) system that traps fuel vapor from the tank. The standard definition is "Evaporative Emission System Leak Detected (Large Leak)."
Can I drive with a P0455 code?
Yes, the vehicle is normally safe to drive and should run as usual. However, a large EVAP leak can release fuel vapor, so check the fuel cap first and get a prompt inspection if you smell raw fuel or see any wetness.
Does a missing gas cap cause P0455?
Yes. Leaving the cap off or loose after refueling is one of the most common causes, and many vehicles will set P0455 or P0457 within a few drive cycles.
What is the difference between P0442, P0455, and P0456?
They describe leak size. P0455 is a large leak, P0442 is a small leak, and P0456 is a very small leak. The bigger the leak, the more likely it is a loose cap or disconnected hose.
Can a bad purge valve set a leak code?
Yes. If the purge valve cannot open during the test, the system never pulls a vacuum, and the computer may interpret that as a large leak.
Keep researching
More emission controls codes
Sources
- SAE J2012 — Diagnostic Trouble Code Definitions (standard code titles)
- ISO 15031-6 — Road vehicles: communication between vehicle and external equipment for emissions-related diagnostics, Part 6: Diagnostic trouble code definitions
- U.S. EPA — Vehicle Emissions Inspection and Maintenance (I/M) programs
- U.S. EPA, 40 CFR 86.1806-17 — Federal onboard diagnostics requirements for light-duty vehicles
- California Air Resources Board — On-Board Diagnostic (OBD) Program
General information written by CarWhere Research, not a diagnosis of your vehicle. Manufacturers can add their own sub-definitions and test conditions; confirm with the factory service information for your year, make and model. Before paying for a repair, check NHTSA for open recalls and your warranty booklet: federal law requires an emissions warranty on major emission-control parts such as the catalytic converter and engine computer.