P0251 - OBD Trouble Code

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Do you see smoke coming out of car’s tailpipe? Is the engine stalling and not starting? Are you experiencing sudden drop in acceleration with inappropriate throttle response? All these can be an indication towards problematic fuel delivery not allowing the fuel to reach the combustion chamber in right amounts, which may lead to OBD code P0251 getting stored in the Powertrain Control Module

If the PCM detects any discrepancy in the signal voltage supplied to the electronic fuel control actuator and in the returning signal from the fuel metering control sensor, OBD code P0251 will be set with the Malfunction Indicator Light (MIL) being illuminated. It is also important to know that this code in specific to diesel powered vehicles only and for vehicles with any other type of propulsion have the biggest chances of PCM failure.

What causes the problem of Injection Pump Fuel Metering Control A Malfunction?

• Contaminated, wrong or bad gasoline
• Optical sensor dirty
• Clogged fuel pump, fuel filter or fuel injector
• Faulty intake air temperature (IAT) sensor, crankshaft position sensor, or accelerator pedal position sensor
• Faulty fuel control actuator
• Faulty Engine Control Module (ECM/PCM)
• Leakage in fuel injector
• A short to power or ground in the wiring related to the intake air temperature sensor, crankshaft position sensor, or accelerator pedal position sensor
• Corrosion on the connectors of the intake air temperature sensor, crankshaft position sensor, accelerator pedal position sensor, fuel injector or related wiring

1. Crankshaft Position Sensor - Check for faults, shortage and corrosion build-up in the crankshaft position sensor and replace it immediately.
2. Throttle Position Sensor - Loss on acceleration, engine stalling and poor throttle response are some of the symptoms indicating this sensor to be faulty. Buy new one and replace it now!
3. Air Temperature Sensor - Check for faults in the air temperature sensor and replace the faulty one. Buy new sensor from us.
4. Optical Sensor - If the optical sensor is faulty, replace it immediately. Buy new sensors from us.
5. Fuel Filter - Damaged or clogged fuel filter will result in contaminated fuel delivery. Replace it immediately.
6. Glow Plugs - Faulty glow plugs will result in engine misfires and not starting in cold weather condition. Replace them now!
7. Spark Plugs - Check for blown fuses and spark plugs and replace them and test the vehicle of proper functioning. These are check repairs and should be done immediately.

Some of the common symptoms associated with OBD Code P0251 are as follows:

Common Symptoms

• Check Engine Light On
• Engine Stalling and misfiring
• Excessive smoke from the exhaust
• Loss of acceleration
• Engine hard or no start condition

Replacement of the following components may solve the OBD code P0251 error.

• Replacing a faulty crankshaft position sensor
• Replacing a faulty accelerator position sensor
• Replacing a faulty intake air temperature sensor
• Replacing a faulty optical sensor
• Cleaning a dirty optical sensor
• Using a fuel treatment which will help clean out deposits or debris within the fuel system
• Replacing a clogged fuel filter
• Replacing a faulty fuel pump
• Replacing faulty glow plugs (diesel only)
• Replacing faulty spark plugs
• Repairing damaged or frayed intake air temperature sensor wiring
• Repairing an open, short to power or ground in the intake air temperature sensor circuit
• Repairing of short, open to power or ground in the accelerator position sensor circuit
• Repairing open, short to power or ground in the crankshaft position sensor circuit
• Replacement a faulty Engine Control Module
• Repairing a short, open to power or ground with the wiring related to the optical sensor

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Following are the diagnostic steps to be followed to resolve OBD code P0251 error;

Check the freeze frame data of the trouble code to determine the values of the optical sensor, crankshaft position sensor, accelerator pedal position sensor, and the intake air temperature sensor.

• Use an OBD scan tool to view the live data feedback of the optical sensor, crankshaft position sensor, accelerator pedal position sensor, and the intake air temperature sensor.
• Make use of a multimeter to check the voltage readings and resistance levels of the optical sensor, crankshaft position sensor, accelerator pedal position sensor, and the intake air temperature sensor.
• Inspects the quality of the fuel and performs a fuel pressure test.
• Also check for damaged or faulty fuel filters, sensors, and circuits.
• Check of wiring and connection and replace if needed.
• If all the components are working perfectly, then doubt the PCM for failure. It may need replacement or reprogramming.

Common Mistakes When Diagnosing The P0251 Code

Most of the time we tend to diagnose the problem without completely identifying the real cause of it. It is important to follow all the diagnostic steps and examine each component carefully before correcting. Some of the components to be focused on are listed below;

• Clogged fuel filter
• Fuel pressure regulator failure
• Fuel pump/injector failure
• Leaking fuel lines
• Powertrain Control Module (PCM) failure
• Wiring/harness issue