Massey Ferguson 521004.11 – Engine ECU: Downstream NOx Sensor Missing / Exhaust Outlet NOx Sensor Missing

The Engine Control Unit (ECU) has lost communication with or cannot detect the downstream NOx sensor (located at the exhaust outlet, after the SCR catalyst). When the signal is missing, the system cannot regulate AdBlue/DEF dosing properly, which will eventually lead to power degradation (limp mode) or engine shutdown to protect the emissions system.

• 7616
• 5612
• 7622
• Interim Tier 4 (2012-2015)
• 7614
• 5611
• 7615
• 5610
• 5613
• 7620
• 5609
• 7618
• 5608
• 7619
• 7626
• 7624
• 5600 Series
• 5700 Series
• 5700 S/SL Series
• 6600 Series
• 6700/6700S Series
• 7700/7700S Series
• 8600 Series
• 8700/8700S Series

1. 1

   Inspect the wiring harness routing to the downstream NOx sensor for melted insulation, chafing, or severed wires.

2. 2

   Disconnect the NOx sensor connector and inspect the pins for water ingress, corrosion, or bent pins.

3. 3

   Using a multimeter, verify that the sensor is receiving proper power and ground, and check the CAN bus communication lines for continuity back to the Engine ECU.

4. 4

   Check the main fuse box for blown fuses related to the emissions system, such as the supply relay for the NOx sensors.

5. 5

   Use a diagnostic scan tool to monitor the downstream NOx sensor live data. If the sensor reads completely blank or static while the upstream sensor is responding, the sensor module has likely failed internally.

1. 1

   Preparation

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

2. 2

   Locate the Sensor

   Locate the downstream NOx sensor, which is threaded into the exhaust pipe after the SCR catalyst/DOC (Diesel Oxidation Catalyst).

3. 3

   Removal

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

4. 4

   Clean the Port

   Clean the threads of the exhaust bung to remove carbon buildup. Ensure no debris falls into the exhaust pipe.

5. 5

   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 can cause immediate failure. Thread it in by hand to prevent cross-threading, then tighten to the OEM torque specification.

6. 6

   Reconnection

   Route the wiring harness exactly as it was from the factory, ensuring it is secured away from direct contact with hot exhaust components. Reconnect the electrical plug.

7. 7

   System Reset

   Reconnect the battery. Connect a diagnostic scan tool, clear the 521004.11 fault code from the Engine ECU, and perform an SCR system test or forced regeneration to verify that the new sensor is communicating and reading NOx levels correctly.