Case IH F-3223-05 - ECU – Engine ECU: Upstream NOx sensor internal failure (Heater Open Circuit Error)

An electrical open circuit in the internal heater of the upstream Nitrogen Oxide (NOx) sensor, indicating the engine controller is detecting zero current flow through the heater circuit.

• MAGNUM AFS Connect
• 240 Series Axial-Flow Combines (7240, 8240, 9240)
• Steiger & Quadtrac Series (470, 500, 580, 620)
• Magnum Series
• Farmall Series (115U)
• Austoft 9900 Sugarcane Harvesters

1. 1

   Locate the upstream NOx sensor in the exhaust pipe directly before the Diesel Oxidation Catalyst (DOC)

2. 2

   Inspect the sensor's wiring pigtail and the main engine harness for chafing, melting, or broken wires

3. 3

   Disconnect the 5-pin MCON connector (C186) and check for pushed-out pins, water intrusion, or corrosion

4. 4

   Using a multimeter, verify that the ECU is supplying the correct voltage and ground to the heater circuit pins on the harness side. If power and ground are present, the sensor's internal heater is definitively burnt out

1. 1

   Cool Down

   Ensure the engine is turned off and the exhaust system (DOC and surrounding pipes) has completely cooled, as the upstream NOx sensor operates in extremely high temperatures.

2. 2

   Disconnect Battery

   Disconnect the negative battery cable to prevent electrical spikes.

3. 3

   Unplug the Sensor

   Disconnect the 5-pin electrical connector linking the upstream NOx sensor to the engine harness.

4. 4

   Remove the Sensor

   Using a specialized NOx sensor socket or a properly sized wrench, carefully unscrew the sensor from the exhaust pipe. Tip: If the sensor is seized, apply penetrating oil to the threads and allow it to soak to prevent stripping the exhaust bung.

5. 5

   Clean the Threads

   Clean the mounting threads in the exhaust pipe with a thread chaser if necessary.

6. 6

   Install the New Sensor

   Thread the new upstream NOx sensor into the exhaust pipe. If the new sensor does not have pre-applied anti-seize, apply a small amount of high-temp sensor-safe anti-seize to the threads (do NOT get any on the sensor probe tip). Torque to the manufacturer's specification.

7. 7

   Reconnect

   Plug the 5-pin connector back into the wiring harness, ensuring the locking tab clicks securely.

8. 8

   Clear Codes

   Reconnect the battery, turn the key to the ON position, and use a diagnostic scan tool to clear the inactive SPN 19051 / F-3223-05 fault code. Start the engine and verify the code does not return.