Case IH 16121 - ATC – ATC (Automatic Temperature Control) module: Temperature select potentiometer open or shorted to power

This fault code indicates an electrical failure in the climate control system. Specifically, the ATC (Automatic Temperature Control) module has detected that the signal from the temperature selection dial (potentiometer) is either an open circuit (broken wire/disconnected) or short-circuited to the positive power supply.

• MAXXUM T4E
• VESTRUM CVX
• Case IH Puma Series: 125, 130, 140, 145, 150, 160, 165, 180, 185, 195, 210, 225 CVX
• Case IH Steiger Series
• Case IH Magnum Series: MX210, MX230, MX255, MX285

1. 1

   Perform a functional test using the ATC display: Activate the 'AUTO' switch and slowly adjust the temperature select control from 16.7°C to 31.1°C (62°F - 88°F) to see if the system registers the input or if data is erratic

2. 2

   Inspect the wiring harness and connectors X755 and X751 (specifically pins A-B) for damage, corrosion, or pushed-out pins

3. 3

   Use a multimeter to check for an open circuit or a short-to-power in the wiring between the temperature potentiometer and the ATC controller

4. 4

   Determine if the failure is isolated to the potentiometer/wiring or if the ATC controller itself has failed and is unable to read the input

1. 1

   Power Down

   Turn off the tractor and disconnect the battery ground to prevent electrical shorts during repair.

2. 2

   Access the HVAC Panel

   Remove the trim panels surrounding the overhead HVAC control module / ATC control panel to access the rear wiring.

3. 3

   Inspect and Clean Connectors

   Disconnect connectors X755 and X751. Inspect them for corrosion, moisture, or loose terminals. Clean the contacts with electrical contact cleaner.

4. 4

   Repair Wiring (If Applicable)

   If your multimeter tests in the diagnostic phase revealed a broken wire or a short to power in the harness, repair or replace the affected section of the AC/ATC wire harness.

5. 5

   Replace the Potentiometer / Control Panel

   If the wiring is intact, the temperature select potentiometer has failed internally. Because the potentiometer is integrated into the control board on modern CNH equipment, you will typically need to replace the entire HVAC / ATC Control Panel assembly.

6. 6

   Reassembly and Clearing Codes

   Plug the connectors into the new ATC control panel, reinstall the overhead trim, and reconnect the battery. Turn the key on, clear the stored fault codes using the electronic service tool or onboard display, and test the climate control to ensure the temperature adjusts correctly.