Case IH 19422 (F-3226-10) – Engine Control Module (ECM) or SCR/DEF system controller (DCU): Downstream NOx sensor signal is stuck at a constant value

The control module is receiving an unchanging reading from the Nitrogen Oxide (NOx) sensor located after the Selective Catalytic Reduction (SCR) catalyst. The system expects the NOx levels to fluctuate based on engine load and DEF (Diesel Exhaust Fluid) dosing; a constant value points to a frozen sensor element, a short in the sensor's internal circuitry, or a communication failure on the CAN bus.

• VESTRUM CVX
• 240 Series Axial-Flow Combines (7240, 8240, 9240)
• 140 Series Combines (5140, 6140, 7140)
• Magnum series (180 through 380)
• Steiger 4WD and Quadtrac series (370 through 620)
• Puma series (150-220)
• Maxxum series (115-150)
• Farmall series (110A-140A)

1. 1

   Check battery voltage, alternator, and alternator belt (low battery voltage is a notorious cause of erratic sensor codes).

2. 2

   Inspect the wiring harness and connector pins leading to the downstream NOx sensor for melted wires, chafing, or corrosion.

3. 3

   Inspect the exhaust piping between the SCR catalyst and the downstream NOx sensor for leaks that could alter exhaust flow.

4. 4

   Verify the DEF quality sensor and DEF dosing valve are operating correctly (if DEF is not injected properly, downstream NOx levels will not change as expected).

1. 1

   Power Down

   Turn off the machine, remove the key, and disconnect the negative battery cable to prevent electrical spikes.

2. 2

   Locate the Sensor

   Locate the downstream NOx sensor on the exhaust system. It is positioned after the SCR catalyst/DPF assembly.

3. 3

   Disconnect Wiring

   Unplug the sensor's electrical connector from the main machine harness.

4. 4

   Remove the Sensor

   Using a specialized NOx/O2 sensor socket or a wrench, carefully unscrew the sensor from the exhaust pipe. (Tip: Exhaust sensors are prone to seizing; apply penetrating oil to the threads and allow it to soak if the sensor is stuck).

5. 5

   Prepare the New Sensor

   Check the threads of the new OEM sensor. If it does not have anti-seize pre-applied, apply a small amount of high-temperature exhaust anti-seize to the threads only. Do not get any anti-seize on the sensor probe tip, as this will instantly ruin it.

6. 6

   Install the New Sensor

   Thread the new sensor into the exhaust pipe by hand to prevent cross-threading, then tighten it to the manufacturer's torque specification.

7. 7

   Reconnect

   Plug the electrical connector back into the harness and secure any loose wiring with zip ties away from hot exhaust components.

8. 8

   Clear Codes

   Reconnect the battery. Use a Case IH Electronic Service Tool (EST) or compatible diagnostic scanner to clear the inactive 19422 / 43CE fault code.

9. 9

   Test Run

   Run the engine up to operating temperature and perform a stationary regen or test drive to verify the ECM is reading fluctuating NOx data and the code does not return.