P0457: A refueling event changes the interpretation of an EVAP gross-leak result

Ford's P0457 monitor is a gross EVAP leak result associated with a refueling event. The familiar “fuel cap loose or off” label reflects that diagnostic context; the controller is evaluating tank pressure behavior rather than physically observing the cap.

Refueling distinguishes this code from the neighboring result

The source lists the same gross-leak pressure criterion for P0455 and P0457, but adds an after-refueling condition to P0457. That difference makes the refueling history relevant evidence. It does not exclude other reasons the system may fail to develop the expected vacuum.

The monitored sequence requires eligible purge operation, fuel level, temperature and driving conditions. The summary also lists fuel-slosh-related abort criteria. A test interrupted by changing tank pressure or fuel level should not be treated as a completed leak evaluation.

Verify the correct phase

Ford's Mode $06 descriptions identify a phase-end pressure result for gross leak/cap-off evaluation and warn that uncompleted phases can display default zero values. The test mapping also changes across model-year strategies, so use the calibration's reported result and limit rather than one assumed identifier.

Check the vehicle's actual fuel-filler arrangement and the relevant diagnostic procedure before selecting a repair. The source supports a refueling-associated sealing concern, but does not prove that every P0457 vehicle has a conventional removable cap or that replacing a cap will resolve the fault.

Source and applicability

This explanation covers the cited Ford monitor variants, not every vehicle displaying this code. Match the engine, sensor architecture and calibration before applying numerical limits.

Ford OBD summary, PDF page 12, Ford OBD summary, PDF page 13, Ford OBD summary, PDF page 14.