New Holland 12111 – INST: Communications Lost with Automatic Temperature Controller

The Instrumentation (INST) controller has lost communication with the Automatic Temperature Controller (ATC) module over the CAN bus network. The INST controller periodically polls the ATC module for its status and logs this fault when it fails to receive a response within a specified time. This prevents proper regulation of in-cab temperature and can disable climate control functions. The underlying cause is typically an electrical or network issue rather than a mechanical failure of the A/C components.

• T6 Series
• T7 Series
• T8 Series
• T9 Series
• CR Series
• CR9080
• Patriot Series
• Trident Series
• Titan Series
• Maxxum
• Quadtrac
• Steiger

1. 1

   Verify battery and system voltage (must be above 12.5V) and ensure the alternator is charging correctly, as low voltage can cause ghost communication codes

2. 2

   Check and clean the main chassis and cab ground connections

3. 3

   Inspect all fuses related to the instrument cluster, cab controller, and HVAC system

4. 4

   Visually inspect the wiring harness and connectors between the instrument panel and the ATC module for chafing, corrosion on pins, pinched wires, or loose connections

1. 1

   Power down the machine

   Turn the ignition key to the OFF position and disconnect the battery. Wait a few minutes for all modules to power down completely.

2. 2

   Locate and disconnect ATC module

   Locate the ATC module, which is often found under the operator's seat. Disconnect its main electrical connector to perform tests.

3. 3

   Perform CAN bus resistance check

   Set multimeter to resistance (Ω). On the main CAN bus harness connector, measure resistance between the CAN High and CAN Low pins. Expected reading is approximately 60 Ω. A reading of ~120 Ω indicates a missing terminating resistor or open circuit. Significantly less than 60 Ω suggests a short circuit. An open circuit (OL) points to a break in the CAN wiring.

4. 4

   Check for shorts to ground or power

   With the connector unplugged, measure resistance from the CAN High pin to a clean chassis ground. Repeat for the CAN Low pin. Both should read as an open circuit (OL) or megaohms. A low resistance reading indicates a short to ground in the wiring harness.

5. 5

   Perform CAN bus voltage check

   Reconnect the battery and turn ignition ON (engine off). Carefully back-probe the ATC module connector while connected. Measure DC voltage between CAN High and ground (expected: 2.5V to 3.0V) and CAN Low and ground (expected: 2.0V to 2.5V). If both are 0V, check power and ground supply to the controllers. If CAN High voltage is lower than CAN Low, the wires may be reversed.

6. 6

   Isolate and replace ATC module

   If the CAN bus wiring tests correctly, the fault may lie with the ATC module itself. Temporarily swap the module with a known good unit to see if the fault clears. If faulty, replace the ATC module.