Case IH 124 – ATC (Automatic Temperature Control): Cab pressure sensor input shorted to ground

The controller monitoring the cab's HVAC and pressurization system is receiving a signal voltage of 0V (or near 0V) from the cab pressure sensor. This underlying condition is typically caused by a pinched or chafed signal wire touching the machine's chassis (ground), moisture in the connector, or an internal dead-short within the sensor itself.

• STX Steiger
• TJ Series (TJ425HD, TJ450HD)
• Steiger series
• Magnum series
• Axial-Flow series (5088, 6088, 7088, 7010, 7120, 8120, 9120)

1. 1

   Visual Inspection: Locate the cab pressure sensor (typically mounted in the cab roof/headliner near the HVAC blower or fresh air intake filter). Inspect the wiring harness for obvious signs of chafing, rodent damage, or pinched wires against the cab frame.

2. 2

   Sensor Isolation Test: Disconnect the electrical connector from the cab pressure sensor. Turn the key to the ON position and check the active fault codes. If the code changes from ATC 124 to ATC 123, the sensor itself is internally shorted. If the code remains ATC 124, the short to ground is in the wiring harness.

3. 3

   Harness Continuity Test: Using a digital multimeter, test the sensor's signal wire for continuity to a known chassis ground. If continuity is present while unplugged from the sensor, trace the harness back to the ATC module to find the short.

4. 4

   Connector Check: Inspect the sensor plug for water intrusion, corrosion, or bent pins, which can bridge the signal and ground circuits.

1. 1

   Power Down

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

2. 2

   Access the Sensor

   Remove the necessary cab headliner panels or exterior HVAC access covers to reach the cab pressure sensor.

3. 3

   Repair Wiring

   If the diagnostic checks revealed a harness short, cut out the damaged section of the wire. Splice in a new section of wire using weather-resistant, heat-shrink butt connectors. Re-wrap the harness in protective loom.

4. 4

   Replace the Sensor

   If applicable, unplug the electrical connector, remove the mounting screws or retaining clips holding the sensor to the HVAC housing, install the new OEM cab pressure sensor and secure it. Plug the electrical connector back in, ensuring the weather seal clicks into place.

5. 5

   Reassembly and Clearing Codes

   Reinstall all cab panels. Reconnect the battery. Turn the key to the ON position and use the AFS Pro monitor (or instrument cluster) to clear inactive fault codes. Start the HVAC system and verify that ATC 124 does not return.