Cummins ISC CM2150 (2007-09) Fault Code: 249 PID: 171 SPN: 171 FMI: 3 Ambient Air Temperature Sensor 1 Circuit – Voltage Above Normal or Shorted to High Source. High signal voltage detected at ambient air temperature circuit.

Verify the electronic control module (ECM) calibration is correct. Check the calibration revision history found on QuickServe® Online for applicable fixes to the calibration stored in the ECM. If necessary, recalibrate the ECM.

The ambient air temperature sensor shares return wires in the engine harness with other sensors. Opens and shorts in the engine harness can cause multiple fault codes to be active. Check active fault codes with multiple counts first.

Possible causes:

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

Possible repairs:

1)Replace the ambient air temperature sensor.
2)Replace the ECM.
3)Repair or replace the engine harness.