Cummins ISB CM850 (2003-06) Fault Code: 553 PID: 157 SPN: 157 FMI: 0 Injector Metering Rail 1 Pressure – Data Valid but Above Normal Operational Range – Moderately Severe Level. The ECM has detected that fuel pressure is higher than commanded pressure.

A fuel pump actuator with excessive leakage or a damaged inboard o-ring will result in high fuel rail pressures at idle or light load.

If the fuel pump actuator exhibits excessive leakage, it is possible that the fuel rail pressure will reach the opening pressure of the fuel rail pressure relief valve and Fault Code 449 may also become active.

Possible repairs:

1)Replace the rail fuel pressure sensor.
2)Replace the fuel gear pump assembly.
3)Replace the damaged o-ring.
4)Replace the fuel pump actuator.