Massey Ferguson 521004.02 – Engine ECU: NOx Sensor Top Of Exhaust Signal Issue / Downstream NOx Sensor Value Implausible

The engine control system has detected that the signal from the downstream (exhaust outlet) NOx sensor is implausible or has failed its plausibility test. This means the sensor is sending data that does not logically align with the engine's current operating conditions or the readings from the upstream NOx sensor.

• 7616
• 5612
• 7622
• Interim Tier 4 (2012-2015)
• 7614
• 5611
• 7615
• 5610
• 5613
• 7620
• 5609
• 7618
• 5608
• 7619
• 7626
• 7624
• 4707
• 4708
• 4709
• 4710
• 5710 SL
• 5711 SL
• 5712 SL
• 5713 SL
• 6700 Series
• 7614 through 7626
• 7714 through 7726
• 8600 Series

1. 1

   Compare Sensor Data: Use a diagnostic tool to monitor both the upstream and downstream NOx sensors. If the downstream NOx reading is flat or erratic while the upstream sensor responds normally to engine load, the downstream sensor is likely at fault.

2. 2

   Check for Exhaust Leaks: Inspect the SCR outlet gaskets and clamps. Fresh joints and tight clamps are required, as exhaust leaks can pull in ambient air and skew the NOx readings.

3. 3

   Inspect the Wiring Harness: Check the wiring and connectors for the downstream NOx sensor. Ensure the harness is routed exactly like the factory setup to avoid heat soak or vibration damage, which are common causes of signal failure.

4. 4

   Check DEF Quality: Ensure the DEF (AdBlue) is not contaminated and the DEF injector is functioning properly, as poor DEF dosing can cause actual NOx conversion failures that trigger plausibility codes.

1. 1

   Preparation

   Turn off the tractor and allow the exhaust system to cool completely.

2. 2

   Disconnect

   Locate the downstream NOx sensor (top of the exhaust/outlet of the SCR catalyst). Disconnect the sensor's electrical connector from the wiring harness.

3. 3

   Removal

   Use a specialized NOx sensor socket or wrench to unthread the sensor from the exhaust pipe.

4. 4

   Clean the Port

   Ensure the mounting threads on the exhaust pipe are clean and free of carbon deposits. Do not use an impact wrench, and do not touch the ceramic probe of the new sensor, as oil contamination from fingers will cause immediate failure.

5. 5

   Installation

   Thread the new NOx sensor into the exhaust pipe and tighten it to the manufacturer's specified torque.

6. 6

   Reconnect

   Plug the sensor back into the wiring harness, ensuring it is routed safely away from extreme heat sources.

7. 7

   Clear Codes

   Connect a diagnostic tool to the tractor and clear the 521004.02 fault code. Run the tractor through a warmup cycle to verify the code does not return.