Dtc P0251

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DTC P0251 - Injection Pump Cam System

The mention of "cam" associated with this code is really a misnomer. The new emissions system monitoring required OBD II to also monitor camshaft position. The 6.5L diesel systems don't monitor cam position, but it gets a "cam" signal in a roundabout way, by optically reading the injection pump's main shaft (which turns at the same rate as the cam). The newer Duramax systems do actually monitor the camshaft position.

This "cam" signal is sensed optically by the optical encoder sensor, which is located in the top portion of the DS fuel injection pump.

So, a P0251 means there is a problem with the OES, which is one of the more important inputs used by the PCM to calculate fuel control and timing.

A P0251 can be caused by air in the fuel system. Bubbles interfere with the optical properties of diesel fuel, which can cause the OES to misread the coded disk as it rotates.

Assuming no air in the fuel, no problem with wiring or electrical connectors, your OES may have an electronic problem (requiring a pump change).

You can read more about P0251 here.

Jim