Massey Ferguson 3218.14 – Engine Control Unit (ECU): Issue With Supply Voltage To NOx Sensor Before DOC

The Engine Control Module has detected that the power supply voltage to the intake (upstream) NOx sensor—located before the Diesel Oxidation Catalyst (DOC)—is either above or below the calibrated threshold.

• 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
• 7714 through 7726S
• 8600 Series

1. 1

   Locate the upstream NOx sensor on the engine exhaust pipe, typically near the turbocharger turbine outlet before the DOC.

2. 2

   Inspect the wiring harness and connectors between the ECU and the upstream NOx sensor for chafed wires, short circuits, open circuits, or corrosion in the pins.

3. 3

   Disconnect the sensor and measure the supply voltage at the harness connector with the key ON to ensure it matches system specifications (typically a 12V/24V supply or a 5V reference).

4. 4

   Check the fuse or relay providing power to the emissions/NOx sensor circuit to ensure it is intact and functioning properly.

5. 5

   Check for an internal sensor short by observing if the supply voltage is correct at the harness but drops significantly when the sensor is plugged in.

1. 1

   Disconnect Power

   Turn off the ignition and disconnect the tractor's battery to prevent electrical spikes.

2. 2

   Repair Wiring

   If the diagnostic checks revealed damaged wiring or a blown fuse, repair the harness and replace the fuse.

3. 3

   Remove the Faulty Sensor

   If the wiring is sound, disconnect the electrical connector from the NOx sensor. Use an appropriate wrench or NOx sensor socket to carefully unscrew the sensor from the exhaust pipe.

4. 4

   Install the New Sensor

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

5. 5

   Reconnect

   Plug in the sensor's electrical connector and reconnect the battery.

6. 6

   Clear Codes and Test

   Use an AGCO Electronic Diagnostic Tool (EDT) to clear the fault code. Start the engine and run it until the DOC intake temperature reaches above 200°C (392°F) for a few minutes. This is the required condition for the ECU to run the diagnostic monitor and verify the repair.