What is the solution for the P0251 trouble code?
2 Answers
p0251 trouble code causes and solutions are as follows: 1. Open circuit in the fuel metering unit drive line. Unplug the fuel metering unit connector, turn the ignition switch to the ON position, and measure the voltage of both pins to ground. Normally, one should be 24V and the other around 3.3V. If there is no voltage, it indicates an open circuit. If both voltages are equal, it indicates a short circuit. Plug in the fuel metering unit, insert a pin from the back end, and measure the voltage of both pins to ground. Normally, both should be 24V. During startup testing, the drive line should be around 0.3V. Measure the resistance of the fuel metering unit; the normal value is 2.6-3.2 ohms. 2. Actual rail pressure is lower than the set rail pressure. Check for leaks or blockages in the low-pressure fuel line (tighten all pipe clamps, check for any folds, ensure the fuel tank is vented, and inspect for any blockages in the fuel tank's pickup tube). Check the fuel injector return flow; normally, the return flow should not exceed the metal plane above the injector's U-clip. Check the fuel injector's injection volume by removing and connecting the injector. If the injector drips during startup, the injector needle valve may be stuck in an open position. Note: For normal injector opening and injection conditions, rail pressure must be greater than 25M. Check if the fuel pump pressure relief valve is stuck in an open position; it can be disassembled and cleaned if necessary.
When the P0251 trouble code lights up, the first thing that comes to my mind is a fuel system control issue, possibly a faulty fuel pump control module or poor wiring connection. I've checked it myself, and common causes include wiring harness short circuits, loose connectors, or control unit failure. The first step is to disconnect the negative battery terminal for a few minutes and then restart to see if the trouble code can be cleared. If the light comes back on, carefully inspect the wiring connections for corrosion or damage. Those with good DIY skills can check the battery voltage and module power supply, but since the circuitry is complex, it's recommended to visit a reliable repair shop for a diagnostic tool check. Ignoring this fault may lead to unstable fuel supply, which is dangerous—like sudden engine stalling while driving. A friend of mine once delayed repairs and ended up stranded on the road, not getting home until late that night. So, once you spot the issue, don’t delay—safety first! Get it checked or repaired immediately to avoid turning a small problem into a big hassle. Nowadays, many vehicle systems are smart, so regular maintenance and checking connection plugs can prevent such faults, especially for older cars that need extra attention.
