Case IH 123 – ATC: Cab pressure sensor input shorted to power

This fault code indicates that the signal voltage returning from the cab pressure sensor to the control module is higher than the maximum expected threshold. This typically means the sensor's signal wire is making direct contact with a power source (a 'short to power'), or the sensor itself has failed internally and is passing full reference voltage back to the controller.

• STX Steiger
• Magnum series (235-340 Series 4)
• Steiger/Quadtrac (TJ425HD, TJ450HD)
• Puma
• Optum
• Maxxum
• Axial-Flow series (5088, 6088, 7088, 7120, 8120, 9120)

1. 1

   Verify the Code: Access the diagnostic menu on the AFS Pro / AFS Pro 700 display to confirm if ATC 123 is an Active code or a Stored code.

2. 2

   Visual Wiring Inspection: Trace the wiring harness from the cab pressure sensor back toward the ATC module. Look for chafed insulation, pinched wires, or areas where the harness rubs against the cab frame.

3. 3

   Connector Check: Disconnect the sensor and inspect the plug for water ingress, bent pins, or corrosion that could bridge the power and signal terminals.

4. 4

   Voltage Test: With the key ON and the sensor disconnected, use a multimeter to probe the signal wire on the harness side. If it reads system voltage (e.g., 12V) or a high reference voltage, the wiring harness is shorted to power. If the voltage is normal, the sensor itself is internally shorted.

1. 1

   Power Down

   Turn off the machine, remove the key, and locate the cab pressure sensor (typically located within the cab roof HVAC assembly or near the fresh air intake filter housing).

2. 2

   Isolate the Fault

   Based on the multimeter test above, determine if the fault is in the harness or the sensor.

3. 3

   Harness Repair (If Applicable)

   If the signal wire is shorted to power, locate the damaged section of the wiring harness. Splice and solder the broken wire, seal it with heat-shrink tubing, and secure the harness away from sharp edges.

4. 4

   Sensor Replacement (If Applicable)

   If the wiring tests good, unbolt/unclip the faulty cab pressure sensor. Install the replacement sensor and plug in the connector.

5. 5

   Clear Codes

   Turn the key to the ON position. Navigate to the diagnostic menu on the AFS display and clear the stored fault codes.

6. 6

   System Test

   Start the machine, turn on the HVAC blower to pressurize the cab, and monitor the display to ensure the ATC 123 code does not return.