Case IH F-3224-06 - ECU – Engine ECU or DCU: Upstream NOx sensor internal failure (Short Circuit Error)

The upstream Nitrogen Oxide (NOx) sensor measures the amount of NOx in the exhaust gases so the system can inject the correct amount of DEF. A 'Short Circuit Error' indicates that the control module has detected an electrical short (either to ground or to a voltage source) within the sensor's internal circuitry or its immediate wiring harness.

• MAGNUM AFS Connect
• Magnum (180, 200, 220, 240, 250, 280, 310, 340, 380)
• Maxxum (115, 125, 135, 145, 150)
• Puma (150, 165, 185, 200, 220)
• Steiger & Quadtrac (370, 420, 470, 500, 540, 580, 620)
• Farmall (110A to 140A)
• Axial-Flow 240 Series (5140, 6140, 7140, 7240, 8240, 9240)
• Patriot (2250, 3240, 3340, 4440)
• Titan (3040, 3540, 4040, 4540)
• Austoft 9900

1. 1

   Inspect the wiring harness leading to the upstream NOx sensor for chafed insulation, melted wires from exhaust heat, or pinched lines that could cause a short circuit

2. 2

   Disconnect the sensor and inspect the pins on both the sensor side and the harness side for water intrusion, corrosion, or bent pins

3. 3

   Verify that the sensor is receiving the correct supply voltage from the ECU/DCU (12V or 24V depending on the machine) alongside a 5V internal reference

4. 4

   Ensure no aftermarket engine tuning chips are installed, as these can intercept and corrupt NOx sensor signals, mimicking an internal failure

5. 5

   Temporarily swap the upstream NOx sensor with a known good sensor to see if the fault code clears or follows the sensor

1. 1

   Power Down

   Turn off the machine and disconnect the battery to prevent any electrical spikes during the repair.

2. 2

   Locate the Sensor

   Find the upstream NOx sensor on the exhaust pipe, located between the turbocharger and the SCR catalyst/DEF doser injector.

3. 3

   Disconnect

   Unplug the electrical connector linking the NOx sensor module to the machine's wiring harness.

4. 4

   Remove the Sensor

   Using a specialized NOx sensor socket or a properly sized wrench, carefully unscrew the sensor probe from the exhaust pipe. Note: Because these sensors endure extreme heat, penetrating oil may be required to free the threads without damaging the exhaust bung.

5. 5

   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 on the threads, apply a high-temperature anti-seize compound (avoiding the sensor tip). Torque to the manufacturer's specification.

6. 6

   Route Wiring

   Reconnect the electrical plug. Ensure the sensor's wiring pigtail is secured and routed away from direct contact with the hot exhaust pipe.

7. 7

   Clear Codes

   Reconnect the battery, turn the ignition on, and use a CNH diagnostic tool (EST) to clear the F-3224-06 fault code. Start the engine and verify the code does not return.