Cummins ISX CM870 (2003-06) Fault Code: 951 PID: 951 SPN: 166 FMI: 2/2 A power imbalance between cylinders was detected by the electronic control module (ECM).

At engine idle speeds, the ECM measures the instantaneous acceleration of each cylinder as it fires to determine the cylinder’s power. The ECM adjusts fueling to individual cylinders if the imbalance is within pre-defined limits. If the imbalance is greater than the pre-defined limits, Fault Code 951 will be set active.

Possible repairs:

1)Check fuel quality.
2)Check for air being ingested into the fuel.