Case IH 3517 (DTC 19C4) - ECU – Engine Control Unit (ECU): Ambient Air Temperature Sensor failure (of Humidity Sensor) - Signal too high

The control module is receiving a voltage signal from the ambient air temperature sensor that exceeds the maximum allowable threshold, indicating an open circuit, a short to a high-voltage source, or an internal failure of the sensor itself.

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1. 1

   Visually inspect the humidity/ambient temperature sensor's electrical connector for disconnected plugs, backed-out pins, moisture, or corrosion.

2. 2

   Inspect the wiring harness leading to the sensor for chafing, cuts, or melted insulation.

3. 3

   Using a multimeter, verify that the sensor ground is intact (an open ground will cause the signal voltage to max out).

4. 4

   Check the signal wire to ensure it is not shorted to a 12V or 5V power source.

5. 5

   Using a diagnostic scan tool, check live data for Ambient Air Temperature. If it reads an impossibly low temperature (like -40°C) or defaults to a maximum voltage value, unplug the sensor. If the voltage drops, the sensor is internally shorted/failed. If the voltage remains high, the wiring harness is shorted to power.

1. 1

   Power down machine

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

2. 2

   Locate the sensor

   The ambient temperature sensor is integrated into the Humidity Sensor. Locate this sensor, typically mounted in the engine air intake tract or the cab HVAC intake.

3. 3

   Disconnect sensor

   Press the release tab on the wiring harness pigtail and disconnect it from the sensor.

4. 4

   Remove faulty sensor

   Unbolt or unclip the faulty humidity/temperature sensor from its mounting point.

5. 5

   Install new sensor

   Install the new OEM replacement sensor and secure it.

6. 6

   Reconnect wiring

   Plug the electrical connector back in, ensuring it clicks and locks into place.

7. 7

   Clear fault codes

   Reconnect the battery, turn the ignition on, and use a diagnostic tool to clear the 3517 / 19C4 fault code from the Engine ECU.

8. 8

   Test operation

   Start the engine and verify that the code does not return and that the engine is no longer in a derated state.