Ambient Air Temperature Sensor 1 Circuit – Voltage Above Normal or Shorted to High Source
|Fault Code: 249
Ambient Air Temperature Sensor 1 Circuit – Voltage Above Normal or Shorted to High Source. High signal voltage detected at ambient air temperature circuit.
None on performance.
ISX and ISM – Ambient Air Temperature Sensor 1 Circuit
The ambient air temperature sensor is used by the electronic control module (ECM) to monitor ambient air temperature. This can be used to sense the temperature inside the cab of a vehicle or the air temperature outside of the vehicle. The ambient air temperature signal is used by the ECM for the Idle Shutdown Ambient Air Temperature Override feature.
The ambient air temperature sensor is used by the ECM to monitor the ambient air temperature. The ambient air temperature sensor is a thermistor and changes resistance based on the temperature being measured. The ECM provides a 5 volt reference voltage to the sensor. The ECM monitors the change in signal voltage and converts this to a temperature value.
The mounting location for the ambient air temperature sensor is OEM dependent. Refer to the appropriate OEM troubleshooting and repair manual.
Conditions for Running the Diagnostics
This diagnostic runs continuously when the keyswitch is in the ON position.
Conditions for Setting the Fault Codes
The ECM detects that the ambient air temperature signal voltage is greater than 4.8-VDC for more than 1 second.
Action Taken When the Fault Code is Active
- The ECM illuminates the amber CHECK ENGINE light immediately when the diagnostic runs and fails.
- A default value for the ambient air temperature reading is used.
- The Idle Shutdown Ambient Air Temperature Override feature will use the intake manifold air temperature sensor value to determine idle shutdown and availability of override.
Conditions for Clearing the Fault Code
The ECM will turn off the amber CHECK ENGINE light immediately after the diagnostic runs and passes.
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. Refer to Procedure 019-032 (ECM Calibration Code) in Section 19 in the corresponding Troubleshooting and Repair Manual for the engine being serviced.
Possible causes of this fault code include:
- Open return circuit in the harness, connectors, or sensor.
- Open signal circuit or shorted to a voltage source.