The P1405 engine code indicates a faulty differential pressure feedback sensor on the Ford Vehicle, according to Engine-Codes.com. This sensor monitors the exhaust gas recirculation tube pressure. When the issue occurs, it triggers the service engine light.
Ford includes the EGR system on the engine to limit the amount of nitrous oxides, or NOx, in the emissions. Redirecting small amounts of exhaust gas into the upper intake allows it to mix with the air and fuel before entering the cylinders. This diluted mixture burns cooler, reducing the combustion chamber temperature and the NOx emissions. In Fords, the power-train control module controls the EGR system, using feedback from the DPFE sensor.
Engine-Codes.com also indicates that Ford has released several service bulletins concerning vehicles with an illuminated service engine light and error code of P1405 which has nothing to do with this sensor. Some Ford Rangers report this code due to an issue with exterior lighting or the ignition module. The Crown Victoria sometimes stores this code for electrical system malfunction. Ford Explorers sometimes store P1405 for other unknown electrical issues.
In locations requiring a smog check of vehicles, the service engine light leads to an automatic fail. Local laws require owners to have the vehicle repaired so the light no longer indicates a malfunction or spend a predetermined amount on repairs.