Case IH F-3234-02 - ECU – Engine Control Module (ECM) or Aftertreatment Control Module (ACM): Downstream NOx sensor lambda signal deviation - NOx sensor possible removal detected

The engine's control system has detected an implausible lambda (oxygen/fuel ratio) signal from the downstream Nitrogen Oxide (NOx) sensor. The system compares this data to the upstream sensor. When the downstream signal deviates significantly from expected parameters, the system suspects that the sensor has been physically removed, tampered with, or has failed completely.

• MAGNUM AFS Connect
• 240 Series Axial-Flow (7240, 8240, 9240)
• 5130/5140
• 6130/6140
• 7130/7140
• Magnum (180 through 380)
• Puma (150 through 220)
• Steiger/Quadtrac (350 through 620)
• Maxxum
• Farmall
• Patriot (2250, 3240, 3340, 4440)
• Titan (3030/3040 through 4530/4540)

1. 1

   Verify that the downstream NOx sensor is physically installed in the exhaust pipe directly after the SCR catalyst. Check the sensor wiring harness and the 5-pin MCON connector for melting, corrosion, or physical damage.

2. 2

   Inspect the exhaust system between the SCR and the downstream NOx sensor for leaks, which can introduce outside air and skew the lambda reading.

3. 3

   Connect a diagnostic tool and view the 'Dew Point' parameter for the NOx sensors. It should read 'Not Ready' during the warm-up cycle until exhaust heat wicks moisture off the sensor tip, after which it must switch to 'Ready'. If it never reaches 'Ready', the sensor's internal heater or the sensor itself has failed.

4. 4

   Compare the downstream NOx sensor readings with the upstream NOx sensor to confirm the deviation.

1. 1

   Preparation

   Turn off the engine and allow the exhaust system and SCR catalyst to cool completely to avoid burns.

2. 2

   Disconnection

   Locate the downstream NOx sensor after the SCR catalyst. Disconnect the electrical connector from the machine's wiring harness.

3. 3

   Removal

   Use a specialized NOx sensor socket or a wrench to carefully unscrew the sensor from the exhaust pipe bung.

4. 4

   Installation

   Apply a high-temperature anti-seize compound to the threads of the new sensor (if it does not come pre-applied). Thread the new sensor into the exhaust bung by hand to prevent cross-threading, then tighten to the OEM specified torque.

5. 5

   Reconnection

   Plug the new sensor's connector back into the wiring harness, ensuring the locking tab clicks into place.

6. 6

   Code Clearing & Reset

   Connect your diagnostic tool and clear the DTCs. Error cleaning is required once after fitting a new NOx sensor.

7. 7

   Validation

   Start the engine and allow it to run through a complete warm-up cycle so the sensor reaches the "Ready" status. Verify that the fault code does not return.