Case IH 3623 – Engine Control Unit (ECU) / CNH EDC: Lambda Signal of NOx Sensor deviation (NOx sensor removal is detected) / Downstream NOx sensor lambda signal deviation

The engine control unit has detected a severe deviation or implausible reading from the downstream NOx sensor's lambda signal. The system interprets this extreme deviation as the sensor either being physically removed, completely disconnected, or having suffered a total internal failure.

• Case IH Steiger series (350 to 600 HP)
• Case IH Magnum series tractors
• Case IH Puma series tractors
• Case IH Maxxum series tractors
• Case IH Axial-Flow Combines (e.g., 240 series, 7230, 8230, 9230)

1. 1

   Check for concurrent active faults involving fueling or air quantity, which can skew exhaust gases and trigger a false NOx sensor deviation

2. 2

   Physically inspect the downstream NOx sensor to ensure it is present, installed correctly, and securely tightened in the exhaust piping

3. 3

   Inspect the NOx sensor wiring harness and connectors for open circuits, short circuits, melted wires from exhaust heat, or corrosion in the connector pins

1. 1

   Verify the Code

   Connect the Electronic Service Tool (EST) or use the onboard diagnostic display to confirm code 3623 is active.

2. 2

   Resolve Preceding Codes

   Clear any air intake, turbocharger, or fueling codes first. If 3623 is the only code, proceed to the sensor.

3. 3

   Inspect and Clean

   Disconnect the NOx sensor harness. Inspect the pins for damage or moisture. Reconnect securely.

4. 4

   Replace the Sensor

   If the wiring is intact, no other fueling/air faults exist, and the fault remains active, the issue is an internal failure of the NOx sensor itself. Remove the faulty downstream NOx sensor from the exhaust and install the replacement.

5. 5

   Clear Codes

   Error cleaning is required after fitting the new NOx sensor. Use the diagnostic tool to clear the DTCs.

6. 6

   Test Run

   Run the machine to operating temperature to ensure the SCR system initializes and the code does not return.