Cummins ISX CM870 (2003-06) Fault Code: 221 PID: P108 SPN: 108 FMI: 3/3 Barometric Pressure Sensor Circuit – Voltage Above Normal or Shorted to High Source. High signal voltage detected at barometric pressure circuit.

The barometric 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 221, check for multiple faults.

Possible causes:

1)Open return circuit in the harness, connectors, or sensor.
2)Signal circuit shorted to sensor supply or battery voltage.

Possible repairs:

1)Repair or replace the engine harness.
2)Replace the barometric pressure sensor.
3)Replace the ECM.