Case IH Tractor ATC 118 Fault Code: Outside Air Sensor Shorted to Ground

Bycaseihfaultcodes

What ATC 118 Means

On a Case IH tractor, fault code ATC 118 is a climate control fault from the ATC controller. The official description is: Outside air sensor shorted to ground.

In practical terms, the ATC controller is seeing an electrical condition that suggests the outside air temperature sensor circuit is connected to ground when it should not be. This may be caused by the sensor itself, the wiring, a connector issue, or less commonly a controller-side problem.

Likely Symptoms

Symptoms can vary by tractor configuration and climate control system behavior. Possible symptoms include:

  • Climate control warning or fault code displayed
  • Automatic climate control performance may be reduced or inconsistent
  • Outside air temperature reading may be missing, incorrect, or unstable
  • Cab heating or cooling decisions may not match actual conditions
  • The fault may return after clearing if the short is still present

Possible Causes

Because ATC 118 specifically points to an outside air sensor circuit shorted to ground, likely causes include:

  • Failed outside air temperature sensor
  • Damaged sensor wiring with the signal circuit touching ground
  • Pinched, rubbed, or crushed harness section
  • Moisture, dirt, corrosion, or damage inside a connector
  • Loose or poorly seated connector terminals
  • Previous electrical repair or accessory installation affecting the circuit
  • Less commonly, an ATC controller input fault

Diagnostic Checks

1. Confirm the Fault

Verify that the active or stored code is ATC 118. If other climate control or electrical faults are present, diagnose them in context rather than assuming the outside air sensor is the only issue.

2. Inspect the Sensor Circuit

Visually inspect the outside air sensor circuit, harness, and connectors where accessible. Look for damaged insulation, rubbed wiring, loose connectors, corrosion, water entry, bent terminals, or signs of prior repair.

3. Check for a Short to Ground

Using the correct service information for the tractor, test the outside air sensor circuit for an unintended path to ground. Do not guess at pin locations or expected readings without the correct wiring diagram.

4. Check Connector Condition

Disconnect and inspect relevant connectors only when it is safe to do so. Contaminated or damaged terminals can create false sensor readings or a ground short condition.

5. Use Live Data if Available

Dealer diagnostic software or a capable diagnostic tool may show the ATC controller’s outside air temperature input. Live data can help confirm whether the controller is receiving a believable signal or a failed/shorted signal.

Repair Guidance

Repairs should be based on test results, not on the fault code alone. Appropriate corrective actions may include:

  • Repairing damaged wiring or harness insulation
  • Cleaning, drying, reseating, or repairing affected connectors
  • Replacing the outside air temperature sensor if testing confirms it is faulty
  • Correcting any wiring damage caused by rubbing, pinching, or previous repairs
  • Clearing the code and confirming that it does not return during operation

If the wiring and sensor test correctly but ATC 118 remains active, further controller-level diagnosis may be needed.

When to Call a Dealer or Qualified Technician

Dealer diagnostic equipment or a qualified technician may be required when:

  • The fault returns immediately after basic inspection or repair
  • Wiring diagrams, connector views, or controller pinout information are needed
  • Live ATC data or guided diagnostic tests are required
  • The suspected issue may involve the ATC controller
  • You are not comfortable testing electrical circuits without causing additional damage

Locate Case IH Parts and Repair Support

Bottom Line

Case IH ATC 118 means the ATC climate control system has detected the outside air sensor circuit shorted to ground. Start with careful inspection of the sensor wiring and connectors, then verify the circuit using the correct service information. Replace parts only after confirming the cause.

Related Diagnostic Guides