Technical Description of OBD-II Trouble Code
There is a malfunction in the Injection Pump Fuel Metering Control A (Cam/Rotor/Injector).
What does that mean?
This generic powertrain/engine diagnostic trouble code can apply to all diesel fueled OBD-II equipped engines (e.g. Ford, Chevy, GMC, Ram, etc.), but it is more common in certain Mercedes Benz and VW vehicles.
Although it is a generic code, the specific repair steps may vary depending on the year, make, model, and powertrain configuration.
The Injection Pump Metering Control Circuit “A” is typically located inside or on the side of the injection pump that is bolted to the engine. It consists of a Fuel Rack Position (FRP) Sensor and a Fuel Quantity Actuator.
The FRP sensor converts the amount of diesel fuel delivered by the Fuel Quantity Actuator to the injectors into an electrical signal for the Powertrain Control Module (PCM).
The PCM uses this voltage signal to determine the amount of fuel to put into the engine based on the operating conditions. This code is set if the input does not match the normal engine operating conditions stored in the PCM’s memory, even for a second. It also checks the voltage signal from the FRP sensor to ensure it is correct at initial Key On.
The code P0251 Injection Pump Fuel Metering Control A Malfunction (Cam/Rotor/Injector) could be set due to mechanical (typically EVAP system mechanical issues) or electrical (FRP sensor circuit) problems. These should not be overlooked during troubleshooting, especially when dealing with an intermittent problem. Consult a vehicle-specific repair manual to determine which part of the circuit corresponds to “A” in your specific application.
Troubleshooting steps may vary depending on the manufacturer, type of FRP sensor, and wire colors.
What is the severity of this DTC?
In this case, the severity is not severe. Since it is an electrical failure, the PCM can compensate adequately for it.
What are some of the symptoms of the code?
Symptoms of a P0251 trouble code may include:
What are some of the common causes of the code?
Causes for this P0251 code may include:
What are some P0251 troubleshooting steps?
A good starting point is always to check for technical service bulletins (TSB) for your vehicle. Your issue may be a known issue with a known fix provided by the manufacturer, which can save you time and money during diagnosis.
Next, locate the FRP sensor on your vehicle. This sensor is usually found inside or on the side of the injection pump that is bolted to the engine. Once located, visually inspect the connector and wiring for any signs of damage. Look for scraping, rubbing, bare wires, burn spots, or melted plastic. Pull the connector apart and carefully inspect the terminals inside for any signs of burning or corrosion. Clean the terminals if necessary using electrical contact cleaner and a plastic bristle brush. Apply electrical grease where the terminals make contact.
If you have a scan tool, clear the diagnostic trouble codes from memory and see if the P0251 code returns. If it does not, then the issue was most likely related to the connections.
If the P0251 code does return, you will need to test the FRP sensor and its associated circuits. With the Key Off, disconnect the electrical connector at the FRP sensor. Connect a Digital Voltmeter black lead to the ground terminal at the FRP sensor wiring harness connector. Connect the red lead of the Digital Voltmeter to the power terminal at the FRP sensor wiring harness connector. Turn the Key On Engine Off and check the manufacturer’s 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 prior test passed, you will need to test the signal wire. With the connector still disconnected, move the red lead of the voltmeter 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 prior tests have passed and you continue to get a P0251, this would most likely indicate a failed FRP sensor / Fuel Quantity Actuator. However, a failed PCM cannot be ruled out until the FRP sensor / Fuel Quantity Actuator has been replaced. If unsure, seek assistance from a trained automotive diagnostician. PCMs must be programmed or calibrated to the vehicle to be installed correctly.
