Massey Ferguson 5026.02 – Engine Control Unit (ECU): Issue With DOC NOx Sensor Module. (ECU)

This code indicates a communication or functional failure with the Nitrogen Oxide (NOx) sensor module located near the Diesel Oxidation Catalyst (DOC). The NOx sensor measures the concentration of nitrogen oxides in the exhaust gases. The engine control system uses this real-time data to regulate the injection of AdBlue (DEF) into the Selective Catalytic Reduction (SCR) system. When the module fails, the system cannot accurately dose DEF, which can lead to emissions non-compliance, increased fuel consumption, and the tractor entering a derated "limp mode".

• 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
• 4607M
• 5608
• 5609
• 5610
• 5611
• 5612
• 5613
• 5708
• 5709
• 5710
• 5711
• 5712
• 5713
• 6612
• 6613
• 6614
• 6615
• 6616
• 6712S
• 6713S
• 6714S
• 6715S
• 6716S
• 6718S
• 7614
• 7615
• 7616
• 7618
• 7619
• 7620
• 7622
• 7624
• 7626
• 8727
• 8730
• 8732
• 8735
• 8737
• 8740
• Activa 7340
• Activa 7344
• Activa 7345
• Activa 7347
• Activa 9540
• Activa 9560

1. 1

   Inspect the wiring harness leading to the DOC NOx sensor module for chafed wires, melted insulation from exhaust heat, or physical damage to the sensor probe.

2. 2

   Disconnect the NOx sensor module connector and check for water intrusion, corrosion, or bent pins.

3. 3

   Verify that the NOx sensor module is receiving proper operating voltage and has a solid ground connection from the ECU.

4. 4

   Inspect the exhaust pipe and DOC housing for leaks upstream of the sensor, as unmetered air can skew NOx readings and trigger module plausibility faults.

5. 5

   Use an AGCO EDT (Electronic Diagnostic Tool) or compatible scanner to monitor live data from the DOC NOx sensor. If the sensor reads a static value, shows no communication, or fails a system plausibility test, the sensor module is likely internally failed.

1. 1

   Preparation

   Turn off the tractor, remove the key, and disconnect the negative battery terminal. Allow the exhaust system to cool completely.

2. 2

   Locate the Sensor

   Locate the DOC NOx sensor on the exhaust aftertreatment assembly (upstream of the SCR catalyst). Note the routing of the sensor's wiring to its integrated control module box.

3. 3

   Removal

   Unplug the electrical connector from the NOx sensor module. Unbolt the module box from its mounting bracket. Using a specialized NOx/O2 sensor socket or a 22mm wrench, carefully unscrew the sensor probe from the exhaust pipe. Tip: If seized, apply penetrating oil and allow it to soak to prevent stripping the exhaust bung threads.

4. 4

   Installation

   Apply a small amount of high-temperature anti-seize compound to the threads of the new sensor (if it does not come pre-applied). Do not get anti-seize on the sensor tip. Thread the new sensor into the exhaust bung by hand to prevent cross-threading, then tighten to the manufacturer's specified torque. Mount the new sensor module box to the bracket and reconnect the electrical harness.

5. 5

   Reset

   Reconnect the battery. Connect a diagnostic scan tool to clear the 005026.02 fault code. Perform an SCR/NOx system reset or calibration procedure if required by the ECU to recognize the new module.