Case IH 3517 (F-171-03) – Engine Control Unit (ECU) / Electronic Diesel Control (EDC): Ambient Air Temperature Sensor failure (of Humidity Sensor) - Signal too high.

The engine control system is receiving a voltage signal from the ambient air temperature circuit (which is integrated into the intake humidity sensor) that exceeds the maximum expected threshold. This indicates an open circuit (such as a broken wire, disconnected plug, or bad ground) or a short to a high-voltage source.

• VESTRUM CVX
• Magnum series (235-340 Series 4)
• Steiger series (350-600)
• Puma
• Optum
• Farmall
• Axial-Flow 240 Series
• Case CE Wheel Loaders (821F, 921F)

1. 1

   Locate the combination Humidity/Ambient Air Temperature sensor on the engine air intake pipe, downstream of the air filter and before the turbocharger.

2. 2

   Check if the sensor is unplugged and inspect the harness connector for moisture, corrosion, or pushed-back pins.

3. 3

   Inspect the wiring harness leading to the sensor for chafing, breaks, or a short to a 5V reference wire.

4. 4

   Connect the CNH EASY diagnostic tool (or compatible scanner) to verify live data for ambient air temperature. An implausible default value (e.g., -40°C or pegged at maximum voltage) with good wiring indicates internal sensor failure.

1. 1

   Power Down

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

2. 2

   Access the Intake

   Locate the humidity/ambient air temperature sensor on the air intake tube. Clean the area around the sensor to prevent dirt from falling into the engine intake.

3. 3

   Disconnect

   Carefully depress the locking tab on the electrical pigtail and disconnect the harness from the sensor.

4. 4

   Remove Sensor

   Remove the mounting fasteners or unclip the sensor and pull it straight out of the intake housing.

5. 5

   Install New Part

   Insert the new humidity/temperature sensor into the intake pipe. Ensure the sealing O-ring is properly seated so unmetered air and dust cannot bypass the air filter. Secure the fasteners.

6. 6

   Reconnect

   Plug the electrical connector back in until the locking tab clicks.

7. 7

   Clear Codes

   Reconnect the battery, turn the ignition on, and use your diagnostic tool to clear fault code 3517. Start the engine and verify that the live ambient temperature reading is accurate and the code does not return.