Why does the Nissan Livina fuel pump have power when unplugged but no power when plugged in?
2 Answers
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.
This issue sounds quite common, I've encountered similar situations several times while repairing cars. When the fuel pump connector of the Nissan Livina is unplugged, there's electricity, but when plugged in, there's none. The main reason might be a circuit short. When the connector is unplugged, if you test the voltage with a multimeter, it shows normal because the circuit is open with no load. However, when plugged in, there might be an internal short in the fuel pump, such as a damaged coil or burnt contacts, causing a sudden surge in current that triggers the protection mechanism, like a blown fuse or circuit disconnection. I suggest you first check the headlight fuse in the fuse box, as the fuel pump circuit often shares a fuse. If that's fine, then test whether the fuel pump relay is stuck—frequent operation can cause overheating protection. Regular maintenance, like cleaning the engine compartment to prevent oil from entering the connector, can reduce such faults. Driving with a fuel pump issue affects fuel supply and can lead to a sudden breakdown, so it's best to address it quickly. I recommend taking it to a professional shop, as DIY attempts might damage more components—safety first.
