Massey Ferguson 3235.05 – Engine ECU: NOx Sensor Outlet SCR Signal Issue

The downstream (outlet) NOx sensor is reporting an 'O2 open wire' or an open circuit in the sensor's measurement signal. The controller is detecting that the electrical circuit to the sensor is incomplete or broken.

• 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
• 4700 Series
• 4710 T4
• 5700 Series
• 5711
• 5712
• 5713
• 6700 Series
• 6711
• 6712
• 6713
• 7700 Series
• 7714S
• 7719S

1. 1

   Locate the downstream NOx sensor (on the exhaust pipe after the SCR catalyst) and visually inspect the wiring harness for cuts, chafing, or heat damage.

2. 2

   Disconnect the NOx sensor connector and inspect the pins for corrosion, moisture, or backed-out terminals.

3. 3

   Use a multimeter to check the continuity of the signal, power, and ground wires between the NOx sensor connector and the Engine ECU harness to confirm if the open wire is in the harness or internal to the sensor.

4. 4

   Turn the key ON (engine off) and verify that the sensor is receiving the correct supply voltage from the ECU.

1. 1

   Power Down

   Turn off the tractor, remove the key, and disconnect the negative battery terminal.

2. 2

   Harness Repair (If Applicable)

   If the diagnostic checks revealed a broken wire or damaged connector in the machine's harness, repair the wiring or splice in a new pigtail connector.

3. 3

   Sensor Removal

   If the harness is intact (meaning the open circuit is internal to the sensor), trace the downstream NOx sensor wire to the exhaust pipe. Disconnect the electrical connector.

4. 4

   Unthread Sensor

   Use a specialized NOx/O2 sensor socket to carefully unthread the faulty sensor from the SCR exhaust pipe.

5. 5

   Install 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 torque to OEM specifications.

6. 6

   Route Wiring

   Reconnect the electrical connector. Ensure the sensor wiring is secured with zip-ties or clips, keeping it safely away from direct contact with the hot exhaust pipe.

7. 7

   Clear Codes

   Reconnect the battery. Connect a diagnostic tool (such as the AGCO Electronic Diagnostic Tool) to the machine, clear the inactive 003235.05 / SPN 3235 FMI 5 fault code, and run the engine to verify the code does not return.