Cummins ISB4.5 CM2150 Fault Code: 451 PID: SPN: 157 FMI: 3 Injector Metering Rail 1 Pressure Sensor Circuit – Voltage Above Normal or Shorted to High Source.

Circuit Description
The fuel delivery pressure sensor responds to pressure changes in the fuel rail. The fuel delivery pressure sensor has a 5 volt supply circuit, a sensor signal voltage, and a return circuit. The electronic control module (ECM) provides a 5 volt supply to the fuel rail pressure sensor, using a common sensor supply circuit. The ECM also provides a ground on the sensor return circuit. The fuel rail pressure sensor provides a signal to the ECM on the fuel rail pressure sensor signal circuit. This sensor signal voltage changes, based on the pressure in the fuel rail. The ECM will detect a low signal voltage at high rail pressures. The ECM will detect a high signal voltage during low rail pressure conditions.

Component Location
The fuel pressure sensor is installed in the fuel rail.

Conditions for Running the Diagnostics
This diagnostic runs continuously when the keyswitch is in the ON position.

Conditions for Setting the Fault Codes
The ECM detects that the fuel rail pressure signal voltage is greater than a calibratible value for more than 1 second. This fault code will become active if there is an open circuit on any of the three pins 5 volt supply, signal, or return that connect the fuel rail pressure sensor or ECM to the wiring harness.

This fault will also be active if the signal wire is shorted to a source of voltage.

Action Taken When the Fault Code is Active
-The ECM illuminates the amber CHECK ENGINE lamp and/or the malfunction indicator lamp (MIL) immediately after the diagnostic runs and fails.
-Engine torque could possibly be reduced.
-A default value for the fuel rail pressure reading is used.

Conditions for Clearing the Fault Code
-To validate the repair, start the engine and let it idle for 1 minute.

For engines equipped with an airless SCR aftertreatment system:
-This fault code can not be cleared with INSITE™ electronic service tool.
-The ECM will turn off the amber CHECK ENGINE lamp and/or MIL immediately after the diagnostic runs and passes.
-Use INSITE™ electronic service tool to verify the fault code is inactive.
-The inactive fault code will be cleared from the memory after 9600 hours of engine operation without a reoccurrence.

For all other engines:
-The ECM will turn off the amber CHECK ENGINE lamp after the diagnostic runs and passes.
-For On-Board Diagnostics (OBD) engines, the ECM will turn off the MIL after three consecutive trips where the diagnostic runs and passes.
-The “Reset All Faults” command in INSITE™ electronic service tool can be used to clear active and inactive faults, as well as extinguish the MIL for OBD applications.

Possible Causes
-Voltage 5-VDC or higher shorted to the signal wire
-Open circuit on the signal wire
-Open circuit on the 5-VDC supply wire
-Open circuit on the return wire
-Malfunctioning sensor
-Malfunctioning ECM.