Massey Ferguson 521005.02 – Engine Control Unit (ECU): NOx Sensor Before DOC Signal Issue

The upstream Nitrogen Oxide (NOx) sensor located before the Diesel Oxidation Catalyst (DOC) in the exhaust system is sending an implausible, erratic, or incorrect signal to the controller.

• 7616
• 5612
• 7622
• Interim Tier 4 (2012-2015)
• 7614
• 5611
• 7615
• 5610
• 5613
• 7620
• 5609
• 7618
• 5608
• 7619
• 7626
• 7624
• 4707
• 4708
• 4709
• 4710
• 5S
• 6S
• 7S
• 8S
• 5700
• 6700

1. 1

   Inspect the wiring harness and connector pins leading to the upstream NOx sensor for chafing, heat damage, vibration wear, corrosion, or moisture

2. 2

   Inspect the exhaust system before the DOC for any leaks, as unmetered air entering the exhaust stream can skew NOx sensor readings

3. 3

   Ensure the DEF tank contains high-quality, ISO 22241-compliant fluid, as contaminated or degraded DEF can cause cascading emissions faults

4. 4

   Check the exhaust pipe and sensor port for excessive carbon deposits that might be blocking the sensor probe

1. 1

   Preparation

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

2. 2

   Removal

   Locate the upstream NOx sensor (between the engine turbo outlet and the DOC). Disconnect the electrical harness connector.

3. 3

   Unthread the Sensor

   Carefully unthread the sensor from the exhaust pipe. Note: Do not use an impact wrench, as this can damage the exhaust bung threads.

4. 4

   Clean the Port

   Clean the mounting threads on the exhaust pipe and ensure no carbon deposits are blocking the port.

5. 5

   Installation

   Thread the new NOx sensor into the exhaust bung by hand to prevent cross-threading, then tighten to the OEM torque specification. Warning: Do not touch the ceramic probe of the new sensor with bare fingers, as oil contamination can cause premature failure.

6. 6

   Routing

   Reconnect the electrical connector. Ensure the harness is routed exactly like the factory setup to avoid heat soak and vibration failures.

7. 7

   Clear Codes

   Reconnect the battery. Use a compatible diagnostic service tool (e.g., AGCO Electronic Diagnostic Tool) to clear the active/inactive faults and reset the SCR system.

8. 8

   Validation

   Perform a diagnostic road/field test under load to ensure the sensor stabilizes and the code does not return.