Cummins ISB CM850 (2003-06) Fault Code: 123 PID: 102 SPN: 102 FMI: 4 Intake Manifold Pressure Sensor Circuit – Voltage Below Normal or Shorted to Low Source. Low signal voltage detected at the intake manifold pressure circuit.

Cummins ISB CM850 (2003-06) Fault Code: 123 PID: 102 SPN: 102 FMI: 4 Intake Manifold Pressure Sensor Circuit – Voltage Below Normal or Shorted to Low Source. Low signal voltage detected at the intake manifold pressure circuit.

The intake manifold pressure sensor shares SUPPLY and RETURN wires in the engine harness with other sensors. Opens and shorts in the engine harness can cause multiple fault codes to be active. Before troubleshooting Fault Code 123, check for multiple faults.

Possible causes:

1)Signal circuit open or shorted to ground in the engine harness or sensor
2)SUPPLY line open or shorted to ground.

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
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 intake manifold pressure sensor.
2)Replace the ECM.
3)Replace the engine harness.