Here is a description of the code and how the system works. You probably have a pump going bad. I have also done a few of the Pump Mounted Driver(PMD's #1 in picture), which is mounted to the side of the pump. They have a relocation kit for them. You can mount it to the wheel well away from heat of the engine. You don't need to remove the old one from the pump, just unplug it.
DTC P0251 Injection Pump Cam Sensor Circuit
The optical sensor provides a pump cam signal to the PCM by counting pulses on the sensor disk located in the injection pump. The pump cam is one of the most important inputs by the PCM for fuel control and timing. This test monitors the number of crankshaft position pulses that have occurred since the last cam pulse. The physical one to one correspondence between the pump cam and the crankshaft implies if more crank pulses are detected than cam pulses, cam pulses have been missed.
Conditions for Running the DTC
- The PCM performs this DTC diagnostic continuously.
- The engine is operating.
Conditions for Setting the DTC
- The number of consecutive missing cam pulses is more than or equal to 8.
- All diagnostic set conditions met for 2 seconds.
Intermittent DTCs (P0251, P0370 and P1216) may be caused by air entering the fuel system when fuel levels get below 1/8 of a tank while performing hard acceleration or turning maneuvers. It's also possible that a P0251, P0370 and P1216 will set the if vehicle has run out of fuel. Customer driving habits should be checked to determine if the vehicle has been performing in these manners. If the vehicle has been performing in these conditions, bleed the fuel system of all air and test drive the vehicle.
When the PCM is in backup fuel, fast idle and poor performance problems will exist.
An intermittent condition can be caused by the following:
- Poor connections.
- Rubbed through wire insulation.
- Broken wire inside the insulation