Cummins ISB6.7 CM2150 (2007-09) Fault Code: 256 PID: 171 SPN: 171 FMI: 4 Ambient Air Temperature Sensor 1 Circuit – Voltage Below Normal or Shorted to Low Source. Low signal voltage detected at the ambient air temperature circuit.
Verify the electronic control module (ECM) calibration is correct. Check the calibration revision history found on QuickServe® Online for applicable...