Cummins ISL CM850 (2003-06) Fault Code: 451 PID: 157 SPN: 157 FMI: 3 Injector Metering Rail Number 1 Pressure Sensor Circuit – Voltage Above Normal or Shorted to High Source. High signal voltage detected at rail fuel pressure sensor circuit.

Cummins ISL CM850 (2003-06) Fault Code: 451 PID: 157 SPN: 157 FMI: 3 Injector Metering Rail Number 1 Pressure Sensor Circuit – Voltage Above Normal or Shorted to High Source. High signal voltage detected at rail fuel pressure sensor circuit.

This fault code will become active if there is an open circuit on any of the three pins (+5 volt SUPPLY, SIGNAL, and RETURN) that connect the sensor or the ECM to the wiring harness. This fault will also be active if the SIGNAL wire is shorted to a source of voltage. This fault code will become inactive any time the keyswitch is ON and the signal returns to a valid in-range voltage.

Possible causes:

1)Voltage (+5-VDC or higher shorted to the SIGNAL wire)
2)Open circuit on the SIGNAL wire
3)Open circuit on the +5-VDC SUPPLY wire
4)Open circuit on the RETURN wire
5)Damaged sensor
6)Malfunctioning ECM.

The sensor return configuration for Euro 4 ISL engines has been changed for automotive wiring harnesses manufactured from February 2012 onward. The new style wiring harnesses can be be identified using the method below:

1)Disconnect the ECM connector
2)Disconnect the camshaft position sensor
3)Disconnect the intake manifold pressure/temperature sensor
4)Check for continuity between the intake manifold pressure/temperature sensor RETURN pin and the camshaft position sensor RETURN pin
5)Check for continuity between ECM pin 47 and the camshaft position sensor RETURN pin
6)Use the table below to determine which harness is fitted to the engine.

NOTE: QSB engines, all C series engines, and all L series engines are not affected by this change.

Possible repairs:

1)Replace the rail fuel pressure sensor.
2)Repair or replace the engine harness.
3)The removal and installation of the connector may correct the fault.
4)Replace the ECM.