Case IH F-171-00 - ECU – ECU / DCU: Ambient temperature sensor voltage is higher than expected

The control module receives a voltage signal from the ambient air temperature sensor that exceeds the maximum expected threshold, indicating an open circuit, a short circuit to a power source, or a completely failed internal sensor component.

• MAGNUM AFS Connect
• 240 Series Axial-Flow Combines
• Steiger Series (350–600 HP)
• Magnum Series
• Puma Series
• Farmall Series (40-45-50 with CVT)
• Case N-Series TLBs

1. 1

   Visually inspect the ambient air temperature sensor housing and electrical connector for physical damage, corrosion, or pushed-out pins.

2. 2

   Check the wiring harness between the sensor and the ECU/DCU for chafed wires shorting to a high-voltage source or a broken wire causing an open circuit.

3. 3

   Verify that the CAN receive signals are communicating properly, as a CAN timeout can sometimes trigger related ambient temperature faults.

4. 4

   Use a multimeter to test the sensor's resistance. If the circuit reads completely open (infinite resistance), the sensor itself has failed.

1. 1

   Power Down

   Turn off the machine, remove the key, and disconnect the negative battery cable to prevent electrical spikes.

2. 2

   Locate and Disconnect

   Locate the ambient temperature sensor. Press the release tab on the electrical pigtail and disconnect the plug.

3. 3

   Harness Repair

   If your diagnostic checks revealed a broken wire or short in the harness, splice and repair the wiring using weather-sealed connectors.

4. 4

   Replace the Sensor

   If the wiring is intact, the sensor is internally faulty. Unbolt or unclip the old sensor from its mounting bracket and install the new OEM replacement part.

5. 5

   Reconnect

   Plug the electrical connector back into the new sensor, ensuring it clicks securely into place. Reconnect the battery.

6. 6

   Clear Codes

   Turn the ignition to the ON position. Use the machine's onboard diagnostic service display or an electronic service tool to clear the inactive fault codes (Code 3517 / 19C4).

7. 7

   Test Operation

   Start the engine and allow it to idle. Verify that the ambient temperature reads correctly on the cab display and that the fault code does not return.