Massey Ferguson 3229.02 – Engine Control Unit (ECU): NOx Sensor Outlet SCR Signal Issue

The Engine ECU is detecting an erratic, implausible, or missing signal from the Outlet NOx sensor. This sensor is located post-catalyst in the Selective Catalytic Reduction (SCR) system and is responsible for reading the nitrogen oxide levels after the exhaust has been treated with Diesel Exhaust Fluid (DEF/AdBlue).

• 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

1. 1

   Inspect the SCR outlet gasket and clamps for exhaust leaks that can skew the NOx readings.

2. 2

   Inspect the NOx sensor wiring harness and connectors for heat soak damage, vibration wear, or corrosion.

3. 3

   Check the fuse/relay assortment for the after-treatment circuits to rule out intermittent power loss.

4. 4

   Verify that the DEF is ISO 22241-compliant and uncontaminated.

5. 5

   Ensure the DEF filter/strainer is clean (replace if over 12 months/1,000 hrs).

6. 6

   Check the DEF injector operation and pump pressure.

1. 1

   Disconnect Power

   Disconnect the tractor's batteries, starting with the negative (-) terminal to prevent electrical shorts.

2. 2

   Locate the Sensor

   Find the Outlet NOx sensor on the exhaust pipe, located downstream of the SCR catalyst.

3. 3

   Disconnect Wiring

   Unplug the electrical connector (1) and carefully disengage the wiring harness (2) from its retaining clips.

4. 4

   Remove the Sensor

   Unscrew the NOx sensor probe from the exhaust pipe.

5. 5

   Remove the Control Unit

   The NOx sensor is hardwired to a small control module. Remove the mounting nuts securing this control unit to the chassis/bracket and remove the entire assembly.

6. 6

   Install the New Sensor

   Install the new sensor probe into the exhaust and mount the new control unit.

7. 7

   Route the Harness

   Route the new NOx sensor harness exactly like the factory routing to avoid future heat soak and vibration failures.

8. 8

   Reconnect

   Plug in the electrical connector and reconnect the battery terminals.

9. 9

   Clear Codes

   Use an AGCO diagnostic tool (EDT) to clear the fault codes and perform an SCR system test or forced regeneration if required by the manual.