Massey Ferguson 3225.03 – Engine Control Unit (ECU): NOx Sensor Before DOC Signal Issue

This indicates a problem with the signal coming from the upstream Nitrogen Oxide (NOx) sensor, which is located in the exhaust stream before the Diesel Oxidation Catalyst (DOC) and Selective Catalytic Reduction (SCR) system. The sensor measures the raw engine-out NOx levels and sends this data to the controller so it can calculate the precise amount of Diesel Exhaust Fluid (DEF) needed for injection. The .03 suffix typically denotes a signal issue, such as a voltage reading that is out of range, erratic, or an open circuit.

• 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
• 5608
• 5609
• 5610
• 5611
• 5612
• 5613
• 5708
• 5709
• 5710
• 5711
• 5712
• 5713
• 6711
• 6712
• 6713
• 6714
• 6715
• 6716
• 6718
• 7614
• 7615
• 7616
• 7618
• 7619
• 7620
• 7622
• 7624
• 7626
• 8727
• 8730
• 8732
• 8735
• 8737
• 8740

1. 1

   Inspect the wiring harness and connector for the upstream NOx sensor for heat damage, chafed wires, water ingress, or corrosion

2. 2

   Remove the sensor and inspect the probe for heavy soot buildup or moisture contamination

3. 3

   Use a multimeter to verify that the sensor is receiving proper supply voltage and has a solid ground

4. 4

   Check for exhaust leaks upstream of the sensor, as escaping exhaust gases or introduced oxygen can skew readings

5. 5

   Use a diagnostic scan tool to monitor live data for the upstream NOx sensor to see if the voltage/ppm readings are dead or fluctuating wildly

1. 1

   Repair Wiring

   If the diagnostic checks reveal damaged wiring or a corroded connector, repair the harness or replace the pigtail connector.

2. 2

   Replace the Sensor

   If the wiring is intact and the sensor has failed internally, replace the upstream NOx sensor. Do not swap the upstream (Before DOC) and downstream (Outlet SCR) sensors as they have unique CAN identification numbers and are not interchangeable.

3. 3

   Reassembly

   Install the new sensor into the exhaust pipe and torque it to the manufacturer's specification. Route the wiring carefully away from extreme heat sources.

4. 4

   Clear Codes and Calibrate

   Connect a diagnostic scan tool to clear the 003225.03 fault code.

5. 5

   Drive Cycle

   Perform a forced SCR system test via the scan tool or run the tractor under load to allow the ECU to validate the new sensor's signal.