The optical sensor provides a pump cam signal to the PCM by counting pulses from the sensor which monitors slots on the data track 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.

The number of consecutive missing cam pulse are greater than or equal to 8.

Important: A jumper wire needs to be made for proper diagnosis of the CAM and High Resolution signal circuits.

1. Use a four inch piece of 20 (.8) gauge wire as the jumper (approximate length).
2. Strip 1/4 inch off the insulation from each end.
3. Crimp a female PCM terminal (part number 12084912) on one end.
4. Crimp an alligator clip (or other holding device) on the other end.

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 if the 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 conditions: