Massey Ferguson 3224.05 – Engine Control Unit (ECU): NOx Sensor Before DOC Signal Issue

The FMI 5 identifier specifically means 'open wire' or 'open circuit'. The system is detecting that the upstream Nitrogen Oxide (NOx) sensor—located before the Diesel Oxidation Catalyst (DOC)—has lost electrical continuity, meaning the sensor is missing, unplugged, or has a severed connection.

• 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
• 5600 Series
• 5700 Series
• 5608-5613
• 5709-5713
• 6600 Series
• 6700 Series
• 6612-6616
• 6712-6718
• 7600 Series
• 7700 Series
• 7614-7626
• 7714-7726
• 8700 Series
• 8727-8740
• 7300 Activa
• BETA series

1. 1

   Locate the upstream NOx sensor (NOx sensor 1) in the exhaust pipe before the DOC and visually inspect the wiring harness for obvious signs of damage, melting, or severed wires.

2. 2

   Disconnect the sensor plug and inspect the pins for corrosion, pushed-back terminals, or water ingress.

3. 3

   Verify that the sensor is receiving proper supply voltage (12V or 24V), ground, and CAN bus communication at the harness connector.

4. 4

   If the harness has continuity back to the ECU and provides the correct voltage/ground, conclude that the open circuit is internal to the NOx sensor probe or its attached control module.

1. 1

   Preparation

   Turn off the machine and disconnect the battery to prevent electrical spikes. Ensure the exhaust system has completely cooled down.

2. 2

   Removal

   Disconnect the electrical connector for the upstream NOx sensor. Carefully unscrew the NOx sensor from the exhaust pipe. Do not use an impact wrench, as this can damage the exhaust bung threads.

3. 3

   Cleaning

   Clean the exhaust pipe threads and remove any carbon deposits from the mounting port to ensure the new sensor seats correctly.

4. 4

   Installation

   Install the new NOx sensor. Crucial Note: Do not touch the ceramic probe of the new sensor with your bare fingers, as oil contamination will cause premature failure. Torque the sensor to the manufacturer's specification (usually hand-tight plus a quarter turn, or specific torque if noted in the manual).

5. 5

   Reconnection

   Plug the sensor's electrical connector back into the machine's harness.

6. 6

   Reset

   Reconnect the battery. Turn the key on and use a diagnostic tool to clear the 003224.05 / SPN 3224 FMI 5 fault code from the ECU. Run the engine to verify the code does not return.