Massey Ferguson 3220.12 – Engine Control Unit (ECU): NOx Sensor Before DOC Signal Issue

The system is receiving an erratic, implausible, or missing signal from 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
• 5700 standard
• 6700 standard
• 6700S
• 7614
• 7615
• 7616
• 7618
• 7619
• 7620
• 7622
• 7624
• 7626
• 7714 through 7726S
• MF 5S
• MF 6S
• MF 7S
• MF 8S

1. 1

   Inspect the wiring harness leading to the upstream NOx sensor for open wires, short circuits, or melted insulation, and ensure the connector is securely seated and free of corrosion or moisture.

2. 2

   Ensure the DEF fluid is a precise 32.5% urea solution and the tank is free of contamination (dirt, diesel, or water).

3. 3

   Remove the sensor and inspect the probe for heavy carbon deposits or oil, which can prevent proper reading.

4. 4

   Inspect the DEF pump module and heated lines for kinks, rub points, or leaks that could cause pressure stabilization faults.

1. 1

   Preparation

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

2. 2

   Removal

   Disconnect the electrical connector for the upstream NOx sensor. Use a specialized NOx sensor socket or wrench to carefully unthread the sensor from the exhaust pipe before the DOC.

3. 3

   Cleaning

   Clean any carbon deposits from the exhaust pipe mounting hole/threads before installing the new sensor.

4. 4

   Installation

   Thread the new NOx sensor in by hand to prevent cross-threading. Do not use an impact wrench, as thread damage will void the warranty. Do not touch the ceramic probe with your bare fingers, as oil contamination from skin will cause premature sensor failure. Tighten to the OEM torque specification.

5. 5

   Reconnection

   Reconnect the sensor's electrical harness and restore battery power.

6. 6

   Code Clearing & Validation

   Connect a compatible electronic service tool (such as the Massey Ferguson/AGCO diagnostic tool) and use the "Reset All Faults" command to clear active and inactive codes.

7. 7

   Road Test

   Perform a diagnostic road test incorporating both steady-state driving and engine load to allow the ECU to run its readiness diagnostics and validate the repair.