Case IH 117 – ATC: Outside air sensor open or shorted to power.

The control module is detecting an abnormal voltage signal from the outside ambient air temperature sensor. An "open" circuit typically means there is infinite resistance (e.g., a broken wire, unplugged connector, or internally failed sensor). "Shorted to power" means the sensor's signal wire is inappropriately making contact with a 12V power source.

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1. 1

   Visually inspect the outside air sensor (located near the cab's fresh air intake or front of the cab roof) and its 2-pin electrical connector for loose connections, backed-out pins, or heavy corrosion.

2. 2

   Trace the wiring harness back toward the ATC module. Look for chafed wires that might be shorting against the frame (short to power) or broken wires (open circuit).

3. 3

   Test the resistance across the sensor's pins using a multimeter. If the multimeter reads infinite resistance (OL), the sensor is internally open and must be replaced.

4. 4

   With the key ON and the sensor unplugged, check the harness side for proper reference voltage from the ATC module.

1. 1

   Disconnect Power

   Disconnect the tractor's battery for a short period. This protects the ATC module from electrical spikes during the repair and may help reset the electronic control systems.

2. 2

   Remove the Faulty Sensor

   Unplug the 2-pin gray secondary lock connector from the outside air sensor. Unclip or unbolt the sensor from its mounting bracket.

3. 3

   Install the New Sensor

   Mount the replacement outside air sensor in the factory location.

4. 4

   Reconnect Wiring

   Plug the 2-pin connector back in, ensuring the secondary lock clicks into place securely.

5. 5

   Clear Codes

   Reconnect the battery. Turn the key ON and test the HVAC system. If the code is stored in the history and the ATC system is still locked out, you may need to clear the ATC DTC errors using a dealer diagnostic tool (EST).