Cummins ISM CM875 (2003-06) Fault Code: 249 PID: P171 SPN: 171 FMI: 3/3 Ambient Air Temperature Sensor 1 Circuit – Voltage Above Normal or Shorted to High Source. High signal voltage detected at ambient air temperature circuit.

Possible causes:

1)Open return circuit in the harness, connectors, or sensor
2)Open signal circuit or shorted to a voltage source.

Possible repair:

1)Replace the OEM harness.
2)Replace the ambient air temperature sensor.
3)Replace the ECM.