P0251 Fuel metering control malfunction of the high pressure fuel pump

OBD-II Trouble Code - P0251 - Data Sheet

Malfunction of the fuel metering control of the high pressure fuel pump (cam / rotor / injector)

What does trouble code P0251 mean?

This Generic Transmission / Engine DTC can usually apply to all OBD-II equipped diesel engines (such as Ford, Chevy, GMC, Ram, etc.), but is more common in some Mercedes Benz and VW vehicles.

Although general, the exact repair steps may vary depending on the model year, make, model, and transmission configuration.

The injection pump "A" metering control circuit is usually located inside or to the side of the injection pump, which is bolted to the engine. The "A" fuel pump metering control circuit typically consists of a fuel rail position (FRP) sensor and a fuel quantity actuator.

The FRP sensor converts the amount of diesel fuel supplied by the fuel quantity actuator to the injectors into an electrical signal to the powertrain control module (PCM).

The PCM receives this voltage signal to determine how much fuel it will put into the engine based on engine operating conditions. This code is set if this input does not match the normal engine operating conditions stored in the PCM memory, even for a second, as this DTC demonstrates. It also checks the voltage signal from the FRP sensor to determine if it is correct when the key is initially turned on.

Code P0251 High Pressure Fuel Pump Fuel Metering Control A malfunction (cam / rotor / injector) could be set due to mechanical (usually EVAP system mechanical problems) or electrical (FRP sensor circuit) problems. They should not be overlooked during the troubleshooting phase, especially when dealing with an intermittent problem. Consult your specific vehicle repair manual to determine which part of the chain is "A" for your specific application.

Troubleshooting steps may vary depending on the manufacturer, FRP sensor type, and wire colors.

What is the severity of this DTC?

The severity in this case will be low. Since this is an electrical fault, the PCM can compensate for it adequately.

What are some symptoms of code P0251?

Symptoms of a P0251 trouble code may include:

• Malfunction Indicator Lamp (MIL) Illumination
• Decreased fuel economy
• Slow start or no start
• Smoke comes from the exhaust pipe
• Engine stalls
• Misfires to a minimum

What are some of the common causes for the code?

Reasons for this P0251 code may include:

• An open in the signal circuit to the FRP sensor - possible
• Short to voltage in the signal circuit of the FRP sensor - possible
• Short to ground in signal circuit to FRP sensor - Possible
• Power or ground break at FRP sensor - possible
• Faulty FRP sensor - probably
• Failed PCM – Unlikely
• Contaminated, incorrect or bad gasoline
• Dirty optical sensor
• Clogged fuel pump, fuel filter or fuel injector.
• Malfunction of intake air temperature sensor, crankshaft position sensor or accelerator pedal position sensor
• Faulty fuel control actuator
• Faulty engine control module
• fuel injector leak
• Short to ground or power in the harness associated with the intake air temperature sensor, crankshaft position sensor, or accelerator pedal position sensor.
• Corrosion on the intake air temperature sensor, crankshaft position sensor, accelerator pedal position sensor, fuel injector connectors or related wiring harnesses

What are some steps to troubleshoot the P0251?

A good starting point is always checking the Technical Service Bulletins (TSB) for your vehicle. Your problem may be a known issue with a known manufacturer-released fix and could save you time and money while troubleshooting.

Then find the FRP sensor on your car. This sensor is usually located inside / on the side of the fuel pump bolted to the engine. Once found, visually inspect the connector and wiring. Look for scratches, scuffs, exposed wires, burn marks, or molten plastic. Disconnect the connector and carefully inspect the terminals (metal parts) inside the connector. See if they look burnt or have a green tint indicating corrosion. If you need to clean the terminals, use an electrical contact cleaner and a plastic bristle brush. Allow to dry and apply electrical grease where the terminals touch.

If you have a scan tool, clear the DTCs from memory and see if P0251 returns. If this is not the case, then there is most likely a connection problem.

If the P0251 code does return, we will need to test the FRP sensor and associated circuits. With the key OFF, disconnect the FRP sensor electrical connector. Connect the black lead from the DVM to the ground terminal on the harness connector of the FRP sensor. Connect the red lead of the DVM to the power terminal on the harness connector of the FRP sensor. Turn on the key, the engine is off. Check manufacturer specifications; the voltmeter should read either 12 volts or 5 volts. If not, repair the power or ground wire or replace the PCM.

If the previous test passes, we will need to check the signal wire. Without removing the connector, move the red voltmeter wire from the power wire terminal to the signal wire terminal. The voltmeter should now read 5 volts. If not, repair the signal wire or replace the PCM.

If all previous tests passed and you continue to receive a P0251, it will most likely indicate a failed FRP sensor / fuel quantity actuator, although the failed PCM cannot be ruled out until the FRP sensor / fuel quantity actuator is replaced. If you are unsure, seek help from a qualified automotive diagnostician. To install correctly, the PCM must be programmed or calibrated for the vehicle.

HOW DOES A MECHANIC DIAGNOSTIC CODE P0251?

• Displays DTC freeze frame data to determine the values ​​of the optical sensor, crankshaft position sensor, accelerator pedal position sensor, and intake air temperature sensor.
• Uses a scan tool to view real-time feedback from the optical sensor, crankshaft position sensor, accelerator pedal position sensor, and intake air temperature sensor.
• Using a multimeter, check the voltage readings and resistance levels* of the optical sensor, crankshaft position sensor, accelerator pedal position sensor, and intake air temperature sensor.
• Check fuel quality
• Performs a fuel pressure test

* The voltage and resistance of each component must comply with the manufacturer's specifications. Specifications will vary depending on the year of manufacture and vehicle model. The specifics for your particular vehicle can be found on a website such as ProDemand or by asking a mechanic.

COMMON ERRORS WHEN DIAGNOSING CODE P0251

There are many things that can trigger a P0251 trouble code. It is important to thoroughly test the components listed as a potential cause of a problem before reporting one as being defective. First, find out which components are applicable to your vehicle. Then check the optical sensor, crankshaft position sensor, accelerator pedal position sensor and intake air temperature sensor, if applicable.

WHAT REPAIRS CAN FIX CODE P0251?

• Replacing a faulty crankshaft position sensor
• Replacing a defective throttle position sensor
• Replacing a faulty intake air temperature sensor
• Replacing a defective optical sensor
• Cleaning a dirty optical sensor
• Using a fuel treatment to help clean deposits or debris from the fuel system.
• Replacing a Clogged Fuel Filter
• Replacing a faulty fuel pump
• Replacing faulty glow plugs (Diesel only)
• Replacing faulty spark plugs
• Repairing any damaged or worn intake air temperature sensor wiring
• Repairing an open, short or high circuit in the intake air temperature sensor circuit
• Repairing a short, open, or ground in the throttle position sensor circuit.
• Repairing an open, short or ground in the crankshaft position sensor circuit
• Replacing a failed engine control module
• Troubleshooting a short, open to ground, or ground in the wiring associated with the optical sensor

ADDITIONAL COMMENTS TO BE AWARE OF CODE P0251

Note that after replacing a failed optical sensor, a scan tool must be used to re-locate the cam setpoints.

P0251 ✅ SYMPTOMS AND CORRECT SOLUTION ✅ - OBD2 Fault Code

Need more help with the P0251 code?

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