Case IH 3518 – Engine Control Unit (ECU / EDC): Ambient Air Temperature Sensor failure (of Humidity Sensor if installed) - Signal too low.

The Engine Control Module (ECM/ECU) is receiving a voltage signal from the Ambient Air Temperature/Humidity Sensor that is below the acceptable minimum threshold. This typically indicates that the sensor's signal circuit is shorted to ground, the sensor itself has failed internally, or (rarely) the ECM has failed.

• Farmall
• skid steer
• Case IH Magnum Tractors 235 - 340 (Series 4)
• Case IH Steiger Tractors 350 - 600
• Case IH Puma Tractors (Puma 210, 240)
• Case IH Windrowers WD1505
• Skid Steer Loaders (SSL)
• Compact Track Loaders (CTL)

1. 1

   Inspect the wiring harness and the connector leading to the Humidity/Ambient Air Temperature Sensor for chafing, corrosion, or pinched wires that could cause a short to ground.

2. 2

   Disconnect the sensor and use a multimeter to check the reference voltage and signal circuit on the harness side. If the signal wire is shorted to ground in the harness, the wiring must be repaired.

3. 3

   If the wiring harness tests fine and shows no shorts to ground, the internal circuitry of the sensor has likely failed and is pulling the signal voltage low.

1. 1

   Power Down

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

2. 2

   Locate the Sensor

   Locate the Humidity and Ambient Air Temperature sensor, which is mounted directly on the engine air intake piping.

3. 3

   Disconnect

   Carefully depress the locking tab and disconnect the electrical wiring harness connector from the sensor.

4. 4

   Remove

   Remove the mounting hardware (screws/bolts) securing the sensor to the intake. Carefully pull the sensor straight out of the intake housing.

5. 5

   Install

   Insert the new sensor into the intake housing, ensuring the O-ring or seal is properly seated to prevent unmetered air leaks.

6. 6

   Secure

   Reinstall and tighten the mounting hardware.

7. 7

   Reconnect

   Plug the electrical connector back into the sensor until it clicks into place.

8. 8

   Clear Codes

   Reconnect the battery, turn the key on, and use a diagnostic scan tool (EST) to clear the 3518 fault code. Start the engine and verify the code does not return.