Case IH 19861 – Engine Control Unit (ECU) or Dosing Control Unit (DCU) / Heater Control Unit (HCU): Signal error for CAN message for upstream temperature sensor

The control module is not receiving a valid CAN bus signal from the exhaust gas temperature (EGT) sensor located upstream of the Diesel Oxidation Catalyst (DOC) or Selective Catalytic Reduction (SCR) unit, preventing the aftertreatment system from properly managing DEF/AdBlue dosing or DPF regeneration cycles.

• Tier 4b
• Farmall
• Maxxum
• Optum
• Puma
• Quantum
• Vestrum
• T7 Series
• Patriot Series
• N-Series Tractor Loader Backhoes

1. 1

   Inspect the wiring harness and connectors between the upstream exhaust gas temperature sensor and the ECU/DCU for melted wires, chafing, corrosion, or loose pins.

2. 2

   Check the CAN bus communication lines (CAN High / CAN Low) at the sensor connector for continuity, shorts to ground, or shorts to power.

3. 3

   Use the CNH Electronic Service Tool (EST) to monitor live data for the upstream temperature sensor. If no communication, check for proper reference voltage and ground at the connector.

4. 4

   Verify if other CAN bus-related fault codes are present to determine if there is a main harness or ECU issue rather than a single failed sensor.

1. 1

   Turn off the machine, remove the key, and disconnect the battery ground cable.

   Ensure the exhaust system has completely cooled down before beginning work.

2. 2

   Locate the upstream exhaust gas temperature sensor.

   It is threaded directly into the exhaust pipe upstream of the DOC/SCR catalyst.

3. 3

   Disconnect the sensor's electrical connector from the main engine harness.

4. 4

   Repair or replace the affected harness section.

   Perform this if wiring damage was found during diagnostics.

5. 5

   Remove the faulty sensor.

   Apply penetrating oil to the sensor threads and allow it to soak. Carefully remove the sensor using a suitable wrench, being careful not to strip the threads in the exhaust pipe.

6. 6

   Apply a high-temperature anti-seize compound to the threads of the new sensor.

   Do this if it does not come pre-applied from the factory to make future removal easier.

7. 7

   Thread the new upstream temperature sensor into the exhaust pipe and torque it to OEM specifications.

8. 8

   Reconnect the electrical connector.

   Ensure the locking tab clicks into place.

9. 9

   Reconnect the battery ground cable.

10. 10

    Clear the fault code and verify the repair.

    Turn the key on and use the CNH EST diagnostic tool to clear fault code 19861. Start the engine and monitor the exhaust temperature live data to verify the sensor is reading correctly and the code does not return.