P0455 on a Ford

What is different about P0455 on a Ford?

Ford's EVAP system design is genuinely different from most competitors, and understanding that difference helps explain some of the documented P0455 causes specific to this make.

What Ford owners run into with P0455

Natural vacuum leak detection (NVLD) system design: Ford's system uses engine-off natural vacuum changes from fuel tank temperature rather than actively pumping the system, a documented distinctly different detection method from most competitors' pump-based EVAP monitors.

Loose or damaged gas cap remains the most common large leak cause: Despite the different detection method, a missing, loose, or damaged gas cap is still documented as the single most common cause of P0455 on Ford vehicles as on any other make.

What to check first on a Ford

The order below narrows the generic P0455 list down to what is worth checking first on this make. It is a starting order, not a diagnosis: patterns are generation specific and a vehicle outside those generations may have none of them.

Check in this order

• Check that the gas cap is present, properly tightened, and its seal is not cracked
• Inspect the NVLD module and associated hoses if the cap is confirmed good
• Inspect the fuel filler neck and hose for cracks or damage
• Check for any obviously disconnected EVAP hoses under the vehicle

The generic picture behind P0455

This code sets when the same sealed system pressure or vacuum test used for the small leak code instead finds a leak large enough to fall into the manufacturer's large leak category, typically equivalent to an opening roughly the size of a small tube or an unsealed cap rather than a pinhole. A large leak is usually something obvious once looked for.

Everything on the main P0455 page still applies here. This page narrows the cause list to the patterns documented on Ford vehicles, it does not replace the underlying definition.

The generic version of this code

• P0455 on any vehicle