Case IH 19422 (DTC 43CE) - ECU – Engine Control Unit (ECU) / Engine Control Module (ECM): Downstream NOx sensor signal is stuck at a constant value.

The downstream NOx sensor output signal is completely static and is not detecting the expected natural fluctuations in exhaust gases. This typically indicates a failed sensor element, a clogged sensor tip (from soot or DEF crystallization), or a wiring harness issue.

• MAXXUM T4E
• 240 Series Axial-Flow (7240, 8240, 9240)
• Magnum series (180 through 380)
• Steiger / Quadtrac series (370 through 620)
• Puma
• Maxxum
• Farmall series
• Patriot series
• Titan series

1. 1

   Check for other active emissions faults (e.g., NH3 or upstream NOx sensor faults) using a diagnostic tool.

2. 2

   Inspect the wiring harness and connector for the downstream NOx sensor for melted wires, chafing, corrosion, or loose connections.

3. 3

   Remove the downstream NOx sensor and inspect the probe tip for heavy soot or white DEF crystals blocking the exhaust flow.

4. 4

   Monitor live data using a diagnostic tool to verify the downstream NOx sensor voltage/ppm reading is completely dead or static while the engine is running.

1. 1

   Power Down

   Turn off the machine and disconnect the batteries or turn off the master disconnect switch to prevent electrical shorts.

2. 2

   Disconnect Sensor

   Locate the downstream NOx sensor (after the SCR catalyst) and disconnect its electrical connector.

3. 3

   Remove Sensor

   Use a NOx sensor socket or a suitable wrench to carefully unscrew the sensor from the exhaust pipe. (Penetrating oil may be required if the threads are seized from exhaust heat).

4. 4

   Install New Sensor

   Apply a small amount of anti-seize to the threads of the new sensor (if not already pre-applied by the manufacturer; do not get anti-seize on the sensor tip). Thread the new sensor into the exhaust pipe and tighten to the OEM torque specification.

5. 5

   Route Wiring

   Reconnect the electrical connector. Ensure the wiring harness is secured with zip-ties or clips and routed safely away from extreme exhaust heat sources.

6. 6

   Reset the ECU

   Reconnect the batteries and turn the key on. Connect your diagnostic tool and clear the inactive fault codes. You must perform an 'Inducement Unlock / Counter Reset' via the diagnostic tool to exit the derated power state.