Massey Ferguson 521016.31 – Engine Control Unit (ECU): NOx Sensor Before DOC Signal Issue

The upstream Nitrogen Oxide (NOx) sensor has recorded a measurement that exceeds the maximum allowable limit (an implausible value or peak check error). The system has detected that the sensor's signal is out of its normal operating range, which can lead to engine power degradation or limp mode.

• 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
• 6712 S
• 6713 S
• 6714 S
• 6715 S
• 7614
• 7615
• 7616
• 7618
• 7619
• 7620
• 7622
• 7624
• 7626
• 8700 S Series
• T CVT Tractors

1. 1

   Inspect the upstream NOx sensor (located before the DOC) for physical damage, heavy soot accumulation, or signs of tampering.

2. 2

   Check the NOx sensor's wiring harness and connector for melted wires, corrosion, open circuits, or short circuits.

3. 3

   Inspect the exhaust piping before the DOC for any leaks, which can introduce excess oxygen or alter exhaust pressure and cause implausible readings.

4. 4

   Look for accompanying codes such as 521017.31 (sensor value stuck) or 5025.31 / 5028.31 (calibration values outside limits) to further confirm a failed sensor element.

1. 1

   Power Down

   Turn off the tractor and disconnect the battery to prevent electrical spikes. Allow the exhaust system to cool completely.

2. 2

   Locate the Sensor

   Locate the upstream NOx sensor in the exhaust pipe, positioned before the Diesel Oxidation Catalyst (DOC).

3. 3

   Disconnect

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

4. 4

   Remove

   Use a specialized NOx/O2 sensor socket or wrench to carefully unscrew the faulty sensor from the exhaust pipe.

5. 5

   Install New Sensor

   Apply a high-temperature anti-seize compound to the threads of the new sensor (if it does not come pre-applied). Thread the new genuine AGCO NOx sensor into the exhaust pipe and tighten to the manufacturer's specified torque.

6. 6

   Reconnect

   Plug the electrical connector back into the harness, ensuring it clicks securely into place.

7. 7

   Clear Codes

   Reconnect the battery. Connect a diagnostic service tool (such as the AGCO Electronic Diagnostic Tool) to the machine and execute the 'Reset All Faults' command to clear the active and inactive codes from the ECU.

8. 8

   Validation Test

   Perform a diagnostic road/field test under load. The engine must reach operating temperature so the ECU can run its internal diagnostics and validate the new sensor's readings.