Massey Ferguson 3234.05 – Engine Control Unit (ECU): Downstream NOx Sensor (Outlet) Current Below Normal or Open Circuit

The system has detected an "open wire" or open circuit error in the downstream (outlet) NOx sensor. This means the control module is not receiving the expected electrical signal from the sensor, which is usually caused by a severed wire, a disconnected plug, or an internal failure of the sensor's circuitry.

• 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
• 5708
• 5709
• 5710
• 5711
• 5712
• 5713
• 6711
• 6712
• 6713
• 6714
• 6715
• 6716
• 6718
• 8727
• 8730
• 8732
• 8735
• 8737
• 8740
• Activa
• BETA

1. 1

   Inspect the wiring harness running from the downstream NOx sensor to the ECU for chafed wires, melted insulation, or physical breaks

2. 2

   Disconnect the NOx sensor plug and check for bent pins, corrosion, water ingress, or loose terminals

3. 3

   Using a multimeter, verify that the sensor connector is receiving proper supply voltage (12V or 24V), ground, and CAN Bus communication signals when the key is ON

4. 4

   If the wiring harness is intact and power/ground/CAN signals are present at the connector, conclude that the open circuit is internal to the NOx sensor module

1. 1

   Preparation

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

2. 2

   Locate the Sensor

   Find the downstream NOx sensor on the exhaust tailpipe, located after the SCR catalyst/DPF assembly.

3. 3

   Disconnect

   Unplug the electrical connector for the NOx sensor from the main engine harness.

4. 4

   Removal

   Use a specialized NOx sensor socket or a properly sized wrench to unscrew the sensor from the exhaust bung.

5. 5

   Clean the Port

   Clean any carbon build-up or debris from the exhaust pipe threads to ensure the new sensor seats correctly.

6. 6

   Installation

   Thread the new NOx sensor into the exhaust bung by hand to prevent cross-threading, then tighten to the manufacturer's specified torque. Do not use an impact wrench, as the vibration will destroy the ceramic element. Do not touch the ceramic probe with your bare fingers or allow it to get contaminated with oil/grease, as this will cause immediate failure.

7. 7

   Reconnect

   Plug the sensor's electrical connector back into the harness and secure the wiring away from extreme heat sources.

8. 8

   Clear Codes

   Reconnect the battery. Use an AGCO diagnostic tool to clear the 003234.05 / SPN 3234 FMI 5 fault code from the ECU.

9. 9

   Test Run

   Start the engine and allow it to reach operating temperature to verify that the SCR system is reading the downstream NOx levels correctly and the code does not return.