Cummins ISB CM850 (2003-06) Fault Code: 951 PID: 166 SPN: 166 FMI: 2 Cylinder power imbalance between cylinders. A power imbalance between cylinders was detected by the ECM.

If Fault Code 951 is inactive in the ECM memory and there is no complaint such as ?low power? or ?engine misfire,? it is possible that an intermittent event such as air entering the fuel system following a filter change caused the fault. Inactive counts of Fault Code 951 should be disregarded unless other performance symptoms are present.

Causes of cylinder imbalance can include:

1)Faulty engine brakes (look for brakes out of adjustment or oil supplied to brake actuator when brakes are off)
2)Valve lash out of adjustment (compare actual valve lash to the reset limits)
3)Cylinder failure (check for high blowby when the engine is loaded)
4)Valve failure or valve held open (listen for intake valve ?chirping? noise in the intake)
5)Cylinder head or gasket failure (look for signs of oil, coolant, or casting flash in the intake or exhaust passages)
6)Extreme camshaft wear (inspect the camshaft lobes for wear)
7)Extra, missing, or damaged sealing washer under an injector
8)Extremely damaged HPC/injector interface (examine the high-pressure fuel connector at the injector end); this problem will also cause excessive fuel return and Fault Code 2292/2216
9)Injector failures (?swap? injectors to see if the problem ?follows? the indicated injector).

Possible repairs:

1)Investigate, diagnose, and correct the condition of the applicable component that is possibly out of adjustment or malfunctioning. ?Swap? injectors between cylinders to see whether or not the problem follows that injector.