What does this code mean?
P0442 describes a small leak, P0455 a large leak and P0456 a very small leak. Check the correct fuel-cap seal where fitted, hoses, valves and the manufacturer's leak-test procedure. A loose cap is one possibility, not the only cause. Do not use compressed air or improvised flame tests around fuel vapour.
Sources and interpretation [1]
A code identifies a detected condition, not a part that must automatically be replaced.
Manufacturer wording
Source wording can vary by vehicle and suffix. It is shown as written, not as a universal diagnosis.
P0455GROSS LEAK DETECTEDP0455EVAPORATIVE EMISSIONS GROSS LEAKManufacturer communications
5Original wording in English
FORD, LINCOLN, MERCURY
Reported code forms P0455
SOME VEHICLES MAY EXHIBIT DRIVEABILITY CONDITIONS AND / OR CHECK ENGINE LAMP ILLUMINATED WITH A DIAGNOSTIC TROUBLE P0455 (GROSS LEAK DETECTED). *TT
FORD, LINCOLN, MERCURY
Reported code forms P0455
SOME VEHICLES MAY EXHIBIT DRIVEABILTY CONDITIONS AND/OR CHECK ENGINE LAMP ILLUMINATED WITH A DIAGNOSTIC TROUBLE CODE P0455 (GROSS LEAK DETECTED). *TT
FORD, LINCOLN
Reported code forms P0455
INFORMATION ON SETTING THE CHECK ENGINE LIGHT AND SETTING DIAGNOSTIC TROUBLE CODE P0455 (EVAPORATIVE EMISSIONS GROSS LEAK). *TT
FORD, LINCOLN
Reported code forms P0455
THIS BULLETIN STATES THAT FOR CERTAIN VEHICLES IT IS NOT POSSIBLE TO SET THE CHECK ENGINE LIGHT AND SET DIAGNOSTIC TROUBLE CODE P0455 (EVAPORATIVE EMISSIONS GROSS LEAK) IF A CUSTOMER REFUELS THE VEHICLE WITH THE ENGINE…
FORD
Reported code forms P0455
CHECK ENGINE LIGHT ON WITH DTC P0455 IN CONTINUOUS MEMORY ON VEHICLE APPLICATIONS. *JD
Check vehicle applicability
6A listed vehicle is a research lead. Confirm the engine, production range and software in the manufacturer's information.
Before replacing a part
Record codes and freeze-frame data. Check battery condition, related codes and visible wiring or hose damage. Follow the vehicle's diagnostic procedure and test results before replacing parts.
Sources and interpretation
These explanations are editorial summaries of the linked manufacturer material. PDF page numbers count from the first file page. Original publications are in English; translations are reference aids. A cited edition is not a claim that it is the manufacturer's latest instruction.
- 2024–2025 MY OBD System Operation Summary for Gasoline Engines ↗
Ford Motor Company · PDF page(s) 11, 12 ·
Source check date · 2026-10-27
Can I keep driving?
A code alone cannot establish whether driving is safe. A flashing malfunction light, severe shaking, overheating, oil-pressure warning or loss of braking or steering needs prompt attention. Stop in a safe place and seek assistance when control or engine safety is affected. Follow the vehicle handbook.