Cummins ISB CM850 (2003-06) Fault Code: 452 PID: 157 SPN: 157 FMI: 4 Injector Metering Rail Number 1 Pressure Sensor Circuit – Voltage Below Normal or Shorted to Low Source. Low signal voltage detected at the rail fuel pressure sensor circuit.

Cummins ISB CM850 (2003-06) Fault Code: 452 PID: 157 SPN: 157 FMI: 4 Injector Metering Rail Number 1 Pressure Sensor Circuit – Voltage Below Normal or Shorted to Low Source. Low signal voltage detected at the rail fuel pressure sensor circuit.

This fault code will become inactive any time the keyswitch is ON and the SIGNAL pin voltage of the ECM is too low. This can be caused by a short circuit to ground on the +5-VDC SUPPLY or SIGNAL wire. This fault will also become active if a device that is powered by the common +5-VDC power supply is shorted to ground. 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)Engine harness: the SUPPLY or SIGNAL wire is shorted to ground
2)Other components: any component connected to the common power supply is shorted to ground
3)Damaged sensor
4)Damaged ECM.

The sensor return configuration for Euro 4 ISB 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
4Check 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.