Case IH F-3232-05 - ECU – Engine ECU: Downstream NOx sensor internal failure (Heater Open Circuit Error)

The engine control system has detected an open electrical circuit in the internal heating element of the downstream Nitrogen Oxide (NOx) sensor, which is required to bring the sensor up to operating temperature quickly.

• MAGNUM AFS Connect
• 240 Series Axial-Flow Combines
• Farmall Tractors (40-45-50 CVT models, etc.)
• Magnum and Steiger Series Tractors
• MX/TG Series Tractors

1. 1

   Locate the downstream NOx sensor in the exhaust stream directly after the Selective Catalytic Reduction (SCR) catalyst.

2. 2

   Inspect the wiring harness leading to the sensor for chafing, melting, or broken wires.

3. 3

   Disconnect the sensor's electrical connector (typically a 5-pin MCON plug) and check for pushed-out pins, corrosion, or moisture intrusion.

4. 4

   Perform a voltage and continuity test to verify that the sensor is receiving proper power and ground from the ECU.

5. 5

   If the wiring harness and connector are in good condition and supplying the correct voltage, the open circuit is internal to the sensor's heater element, and the sensor must be replaced.

1. 1

   Preparation

   Turn off the machine, remove the key, and disconnect the battery to prevent electrical shorts. Allow the exhaust system to cool completely.

2. 2

   Disconnection

   Locate the downstream NOx sensor on the tailpipe/exhaust outlet (after the DOC and SCR). Unplug the sensor's electrical connector from the main engine harness.

3. 3

   Removal

   Using a specialized NOx sensor socket or a suitable wrench, carefully unscrew the faulty NOx sensor from the exhaust pipe bung.

4. 4

   Installation

   Apply a small amount of anti-seize compound to the threads of the new sensor (if not pre-applied from the factory), being extremely careful not to get any on the sensor probe itself. Thread the new sensor into the exhaust pipe and tighten to the manufacturer's specified torque.

5. 5

   Reconnection

   Plug the new sensor's electrical connector back into the machine's wiring harness.

6. 6

   Clear Codes

   Reconnect the battery. Connect a diagnostic scan tool to the machine and clear the inactive fault codes.

7. 7

   Verification

   Start the engine and allow it to reach normal operating temperature. Verify that the warning lights remain off and that the SCR system is dosing correctly without triggering a derate.