Cummins ISX CM870 (2003-06) Fault Code: 559 PID: P157 SPN: 157 FMI: 1/18 Injector Metering Rail 1 Pressure – Data Valid But Below Normal Operating Range – Moderately Severe Level. The engine control module (ECM) has detected that fuel pressure is lower than commanded pressure.

The ECM estimates the amount of fuel delivered to each bank by monitoring the crankshaft acceleration pattern as it rotates. This fault is set active if the ECM estimates that the front bank is receiving insufficient fuel flow.

Possible repairs:

1)Install the original front fueling actuator.
2)Replace the o-rings.