Case IH 3623 (F-3234-02) – Engine Control Unit (ECU): Downstream NOx sensor lambda signal deviation - NOx sensor possible removal detected

The engine control system has detected an implausible signal or a severe deviation from the downstream Nitrogen Oxide (NOx) sensor. The reading is so far out of the expected physical range that the system suspects the sensor has either completely failed, its wiring has been severed, or the sensor has been physically removed/tampered with to bypass the emissions system.

• VESTRUM CVX
• 240 Series Axial-Flow Combines
• Steiger Series Tractors
• Farmall Series Tractors
• Magnum Series Tractors

1. 1

   Check the ECU for any other active fault codes related to fueling or air quantity. Correct these first, as improper mixtures will skew exhaust output and trigger a false NOx deviation code.

2. 2

   Visually inspect the downstream NOx sensor (located on the exhaust piping after the SCR catalyst) to ensure it is physically installed correctly and has not been removed or bypassed.

3. 3

   Inspect the wiring harness and the connector leading to the downstream NOx sensor for melted wires, corrosion in the pins, or open/short circuits.

1. 1

   Turn off the machine, disconnect the battery, and allow the exhaust system to cool completely.

2. 2

   Locate the downstream NOx sensor on the exhaust pipe (post-SCR catalyst).

3. 3

   Disconnect the electrical connector for the NOx sensor.

4. 4

   Carefully unscrew the faulty NOx sensor from the exhaust piping.

   Penetrating oil may be required if the threads are seized.

5. 5

   Install the new NOx sensor and tighten it to the manufacturer's specified torque.

6. 6

   Route the wiring safely away from extreme heat sources and reconnect the electrical plug.

7. 7

   Reconnect the battery and use an Electronic Service Tool (EST) or the on-board diagnostic display to clear the fault codes.

   Error clearing is required after fitting a new NOx sensor to reset the SCR system logic.