Case IH 136 – ATC (Automatic Temperature Controller): Defog light output fault (overcurrent, short to ground)

The system has detected an electrical anomaly on the circuit responsible for illuminating the defog indicator light. Specifically, the circuit is drawing excessive electrical current or has a direct short to the chassis ground.

• STX Steiger
• Magnum series
• MX180
• MX200
• MX220
• MX240
• MX285
• Steiger series
• Puma series
• Maxxum series
• Axial-Flow 2588
• Axial-Flow 5088
• Axial-Flow 5130
• Axial-Flow 6088
• Axial-Flow 7088
• Axial-Flow 7120
• Axial-Flow 7130
• Axial-Flow 8010
• Axial-Flow 8120
• Axial-Flow 8230
• Axial-Flow 9010
• Axial-Flow 9240
• Axial-Flow AFX8010

1. 1

   Perform a functional test by turning the key on and pressing the defog switch to observe if the defog light illuminates or if the A/C compressor engages.

2. 2

   Inspect the wiring harness running between the ATC Control Module and the cab climate control panel for chafed insulation, pinched wires behind cab trim panels, or exposed copper touching the metal cab frame.

3. 3

   Disconnect the climate control switch panel and the ATC module, then use a multimeter to check for continuity between the defog light output wire and a known good ground to identify a short.

4. 4

   Test the defog switch/light assembly itself for an internal short circuit.

1. 1

   Disconnect Power

   Always disconnect the machine's battery before performing electrical repairs to prevent further module damage.

2. 2

   Access the Components

   Remove the necessary cab trim panels to access the rear of the climate control panel (where the defog switch is located) and the ATC module.

3. 3

   Repair the Short

   If the multimeter test revealed a short in the wiring harness, locate the damaged section. Cut out the damaged wire, splice in a new section, and seal it with heat-shrink tubing, or replace the affected harness section entirely. If the short is internal to the switch, replace the defog switch/climate control panel assembly.

4. 4

   Replace the ATC Module (if necessary)

   If the wiring harness and switch test perfectly fine, the output driver inside the ATC module has likely failed internally. Remove the mounting hardware and wiring connectors from the ATC module and install a replacement unit.

5. 5

   Clear Fault Codes

   Reconnect the battery and turn the ignition on. Use the AFS Pro monitor or the tractor's diagnostic interface to clear the controller fault.

6. 6

   Verify Repair

   Press the defog switch. Ensure the defog light turns on, the A/C compressor engages, and the ATC 136 code does not return.