Massey Ferguson 3220.02 – Engine Control Unit (ECU): NOx Sensor Before DOC Signal Issue

The Engine Control Unit (ECU) has detected that the signal from the Nitrogen Oxide (NOx) sensor located before the Diesel Oxidation Catalyst (DOC) is missing, out of the expected range, or malfunctioning. This sensor measures the concentration of nitrogen oxides in the raw exhaust gas to provide critical data for the Selective Catalytic Reduction (SCR) system. A failure in this signal can lead to incorrect DEF injection, increased emissions, higher fuel consumption, and potential engine derates or 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
• 5608
• 5609
• 5610
• 5611
• 5612
• 5613
• 7614
• 7615
• 7616
• 7618
• 7619
• 7620
• 7622
• 7624
• 7626
• 7714S
• 7719S

1. 1

   Inspect the wiring harness and connector leading to the upstream NOx sensor for chafing, melting, or corrosion (related codes SPN 3218, 3222, 3224, or 3225 indicate electrical issues).

2. 2

   Check for exhaust leaks in the piping before the DOC, which can introduce unmetered oxygen and skew sensor readings.

3. 3

   Inspect the sensor for heavy soot or DEF crystal buildup, which can cause stability issues.

1. 1

   Power Down

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

2. 2

   Locate the Sensor

   Locate the upstream NOx sensor. It is threaded into the exhaust pipe before the Diesel Oxidation Catalyst (DOC).

3. 3

   Disconnect

   Unplug the electrical connector linking the NOx sensor to the engine wiring harness.

4. 4

   Remove the Sensor

   Carefully unscrew the NOx sensor from the exhaust bung. (Tip: Use penetrating oil if the sensor is seized to avoid stripping the exhaust pipe threads).

5. 5

   Install the New Sensor

   Thread the new genuine AGCO NOx sensor into the exhaust bung and tighten it securely.

6. 6

   Reconnect

   Plug the new sensor's electrical connector back into the harness.

7. 7

   Clear Codes

   Reconnect the battery. Connect the AGCO Electronic Diagnostic Tool (EDT) to the tractor's diagnostic port to clear the 003220.02 fault code and reset the aftertreatment system's learned values.

8. 8

   Test Run

   Run the tractor to operating temperature to ensure the SCR system stabilizes and the code does not return.