Massey Ferguson 5025.31 – Engine Control Unit (ECU): NOx Sensor Before DOC Calibration Code Issue

The system has detected a calibration failure, implausible signal, or electrical anomaly with the upstream Nitrogen Oxide (NOx) sensor, which is located in the exhaust stream before the Diesel Oxidation Catalyst (DOC).

• 4710
• 7724S
• 5712SL
• 7722S
• 7722
• 5713SL
• 7720S
• 7716
• 7718
• T4
• 7715
• 5710SL
• 7726
• 4708
• 7726S
• 4707
• 4709
• 5711SL
• 7718S
• 7719
• 7714
• 7716S
• T4 (2015-2021)
• 7720
• Tier 4 (2015-2021)
• 7715S
• 7724
• 5608
• 5609
• 5610
• 5611
• 5612
• 5613
• 7614
• 7615
• 7616
• 7618
• 7619
• 7620
• 7622
• 7624
• 7626

1. 1

   Inspect the wiring harness and connector for the upstream NOx sensor (Sensor 1) for chafing, melted wires, corrosion, or loose pins.

2. 2

   Inspect the exhaust piping before the DOC for any leaks. Unmetered oxygen entering the exhaust stream before the sensor can skew the readings and trigger calibration faults.

3. 3

   Remove the sensor and check the probe for heavy soot or carbon deposits, which can blind the sensor.

4. 4

   Use the AGCO EDT (Electronic Diagnostic Tool) to monitor live data. Check if the sensor is reporting open circuits, short circuits, or implausible values (e.g., maximum heating time exceeded).

1. 1

   Cool Down

   Ensure the tractor engine is turned off and the exhaust system has completely cooled down to prevent severe burns.

2. 2

   Disconnect Power

   Disconnect the tractor's battery to prevent electrical shorts during the repair.

3. 3

   Locate the Sensor

   Locate the upstream NOx sensor, which is threaded into the exhaust pipe before the DOC assembly.

4. 4

   Disconnect Wiring

   Unplug the electrical connector linking the NOx sensor to the main engine harness.

5. 5

   Remove the Sensor

   Use a specialized NOx sensor socket or wrench to carefully unscrew the sensor. Do not use an impact wrench, as this can damage the exhaust threads.

6. 6

   Clean the Port

   Clean the mounting threads on the exhaust pipe, ensuring no carbon deposits or debris fall into the exhaust stream.

7. 7

   Install the New Sensor

   Thread the new NOx sensor into place. Crucial Note: Do not touch the ceramic probe of the new sensor with bare fingers, as oil contamination will cause premature failure. Tighten to the OEM specified torque.

8. 8

   Reconnect

   Plug in the electrical connector and reconnect the battery.

9. 9

   Clear Codes & Calibrate

   Connect the AGCO EDT diagnostic tool to clear the 005025.31 fault code. A startup cycle or software reset may be required to calibrate the new sensor to the ECU.