A 2010 Nissan NV400 arrives in the bay with a crank-no-start condition and a single fault code, P0627. The engine control unit on this 2.3 dCi (M9T) is flagging an open circuit in the fuel pump control system, meaning the low-pressure lift pump is completely dead.
Evaluating the fuel pump relay
The most common culprit for this code on this specific vehicle, ranked at 42 percent in our data, is a defective fuel pump relay. Located in the underhood fuse and relay box (UPC), this relay supplies main voltage to the electrical pre-pump in the fuel tank. The ECU monitors the control and actuator circuits. If the internal coil fails or the working contacts burn out, the ECU detects the open circuit and logs P0627. Without fuel delivery, the high-pressure pump cannot build the required 250 bar to start the engine.
To verify this, start with a simple click and activation test at ignition on. Measure the resistance of the relay coil winding. You can also bypass the relay socket contacts with a jumper wire to force the pre-pump to run.
Tracing the chassis wiring harness
If the relay is functioning, the diagnostic path moves under the vehicle. Ranked at 32 percent likelihood is a break or severe corrosion in the wiring harness connecting the UPC to the tank armature. On the Nissan NV400, this harness runs exposed under the chassis. The wiring and the connector on top of the fuel tank take a beating from gravel, road salt, vibration, and moisture. Chafing against the chassis rails or internal corrosion in the connector terminals creates an open circuit or high resistance.
Confirming a wiring fault requires measuring voltage under load right at the tank armature connector. Measure the voltage drop and verify the resistance on the ground wire to the chassis. A thorough visual inspection of the connector and the harness routing along the frame is also necessary.
Testing the lift pump and power supply
An internal failure of the electric pre-pump itself accounts for 24 percent of these cases. Normal wear or overheating can completely wear down the carbon brushes or burn the armature winding. This creates a permanent internal open circuit. Since no current flows when the relay closes, the ECU flags the same P0627 code. Test this by measuring resistance directly across the pump pins at the armature, or apply a direct 12V external power supply to the pump. Monitoring rail pressure in live data during cranking will quickly confirm the lack of fuel delivery.
Finally, a blown fuse or an internal voltage drop inside the UPC module represents 18 percent of cases. If the dedicated pump fuse blows from a temporary overload, or if the internal busbar suffers oxidation, the relay socket will not receive power at pin 30. Visually and electrically check the fuel pump fuse, and measure for battery voltage at the relay socket with the ignition turned on.
What to check first
When diagnosing a crank-no-start NV400 with a P0627 code, start at the underhood relay box. Bypassing the fuel pump relay at the socket immediately splits the circuit in half. If the pump runs with a jumper wire, the wiring and pump are intact, pointing your diagnosis back toward the relay or the UPC module. If it remains silent, you know the fault lies under the vehicle in the chassis harness or the tank armature itself.
Reference pages for the codes in this article
- P0627: what we measure for this code across real diagnostics
