Massey Ferguson 3230.02 – Engine Control Unit (ECU): NOx Sensor Outlet SCR Signal Issue

The system is detecting an abnormal, erratic, or implausible signal from the downstream (outlet) NOx sensor. This sensor is located in the exhaust stream after the Selective Catalytic Reduction (SCR) catalyst. Its job is to measure the amount of nitrogen oxides remaining in the exhaust after the DEF (AdBlue) fluid has been injected and processed by the catalyst. An erratic signal usually indicates a failing sensor probe, a damaged sensor control module, or an exhaust leak skewing the readings.

• 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
• 6612
• 6613
• 6614
• 6615
• 6616
• 6711
• 6712
• 6713
• 6714
• 6715
• 6716
• 6718
• 7614
• 7615
• 7616
• 7618
• 7619
• 7620
• 7622
• 7624
• 7626
• 8727
• 8730
• 8732
• 8735
• 8737
• 8740
• 7340
• 7344
• 7345
• 7347
• 7360
• 7370

1. 1

   Inspect the SCR outlet gasket and clamps for exhaust leaks, as fresh air entering the exhaust stream will skew NOx readings and trigger a false code

2. 2

   Inspect the NOx sensor wiring harness for heat soak damage, melted wires, or vibration chafing, and ensure it is routed exactly as it was from the factory

3. 3

   Check the fuse and relay assortment for the after-treatment circuits to rule out intermittent power drops to the sensor module

4. 4

   Ensure the DEF (AdBlue) is clean and the DEF filter/strainer is not clogged, as poor DEF injection can cause erratic downstream readings

1. 1

   Power Down

   Turn off the ignition and wait for the aftertreatment system to complete its purge cycle (listen for the DEF pump to stop clicking/whining). Disconnect the battery to prevent electrical spikes.

2. 2

   Locate the Sensor

   Locate the downstream NOx sensor on the exhaust pipe, positioned after the SCR catalyst.

3. 3

   Disconnect Wiring

   Unplug the electrical connector from the NOx sensor's control module box.

4. 4

   Remove the Sensor

   Using a specialized NOx/O2 sensor socket (usually 22mm or 7/8"), carefully unscrew the sensor probe from the exhaust pipe. If it is seized, apply penetrating oil and allow it to soak to prevent stripping the exhaust bung threads.

5. 5

   Install the New Sensor

   Thread the new sensor into the exhaust bung. If the new sensor does not have anti-seize pre-applied to the threads, apply a small amount (ensure absolutely none gets on the sensor tip). Torque to OEM specifications.

6. 6

   Route the Harness

   Secure the sensor module and route the wiring harness exactly along the factory path. Keep it away from direct heat sources and sharp vibrating edges.

7. 7

   Clear Codes

   Reconnect the battery. Use an AGCO EDT (Electronic Diagnostic Tool) or equivalent heavy-duty scanner to clear the 003230.02 fault code.

8. 8

   Test Run

   Run the tractor under load to bring the exhaust up to operating temperature so the SCR system activates and verifies the new sensor signal.