Case IH 3623 (DTC 3CAE) - ECU – Engine Control Module (ECM) / Engine ECU: Downstream NOx sensor lambda signal deviation - NOx sensor possible removal detected.

This code indicates that the engine management system has detected an abnormal lambda (oxygen/exhaust gas) signal from the downstream NOx sensor. The system continuously monitors these sensor values; if the signal deviates significantly from expected operating ranges, the system flags a 'possible removal detected,' meaning it suspects the sensor has been physically removed, bypassed, or has failed completely.

• MAXXUM T4E
• Case IH 240 Series Axial-Flow® Combines
• Case IH Farmall Tractors (40-45-50 models with Cab/CVT and Farmall 115U Efficient Power)
• Case IH Wheel Loaders (1021G Tier 4B)

1. 1

   Visual Inspection for Tampering: Physically verify that the downstream NOx sensor is actually installed in the exhaust pipe directly after the SCR catalyst.

2. 2

   Wiring and Connector Check: Inspect the engine and rear chassis harness. Check the 5-cavity female wire connector for disconnected plugs, corroded pins, or severed wires.

3. 3

   Data Comparison: Using a diagnostic tool, compare the data from the downstream NOx sensor to the upstream NOx sensor.

4. 4

   Check for Related Codes: Look for accompanying codes related to ECM internal failures, SCR temperature sensor drift, or AdBlue/DEF dosing issues.

1. 1

   Locate the Sensor

   Find the downstream NOx sensor on the exhaust system, located directly after the SCR catalyst.

2. 2

   Secure or Reinstall

   If the sensor is loose or has been removed, reinstall it securely into the exhaust bung.

3. 3

   Repair Harness

   If the 5-cavity female connector or wiring harness is damaged, repair the wiring to restore communication to the ECM.

4. 4

   Replace the Sensor

   If the sensor is physically present, the wiring is intact, and the lambda signal is still reading as a deviation/removal, the sensor itself has failed internally and must be replaced.

5. 5

   Clear Codes

   After replacing the sensor or repairing the connection, use a diagnostic tool to clear the DTC 3CAE (3623) from the ECM. The system may require a run cycle to verify SCR efficiency and confirm the repair.