Why does the Nissan Livina fuel pump have power when unplugged but no power when plugged in?

[OGraham]

This is because the voltage between the two wires is equal (the power line and the return line are connected through the motor coil), resulting in no voltage drop. This is normal. If the fuel pump is not working, check whether the grounding wire of the return line has poor contact. Principle of the fuel pump: The fuel pump is a lightweight and compact pump. It features a housing made of aluminum-containing material and a movable molded part inside the housing. The movable molded part is at least partially made of a sinterable, iron-based alloy material containing at least one austenitic component. Additionally, the sinterable material of the molded part has a thermal expansion coefficient that is at least 60% of that of the housing. Classification of fuel pumps: Fuel pumps can be divided into three main categories: in-line, distributor, and unit pumps. The amount, pressure, and timing of fuel delivery must be very precise and automatically adjusted according to the load. The fuel pump is a finely processed and complex component, and fuel pumps for automotive diesel engines, both domestically and internationally, are generally produced by a few specialized manufacturers worldwide.