Massey Ferguson 521026.31 – ECU: SCR NOx Levels Too High (ECU)

The Selective Catalytic Reduction (SCR) system is failing to reduce Nitrogen Oxide (NOx) emissions to the acceptable threshold. This code is triggered when the NOx sensor detects that emissions are still too high post-catalyst, which will eventually lead to engine derates.

• 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
• 5709
• 5710
• 5711
• 5712
• 5713
• 6711
• 6712
• 6714
• 6715
• 6716
• 6718
• 7614-7624
• 7714-7726
• 8670
• 8680
• 8690
• 8727
• 8730
• 8732

1. 1

   Verify DEF quality in the tank for contamination (dirt, diesel, water) or crystallization

2. 2

   Inspect the DEF tank, pump module, heated supply/return lines, and O-rings for leaks, kinks, or rub points

3. 3

   Test the dosing system using a diagnostic tool to verify the DEF doser/injector is operating correctly and the pump is building adequate pressure

4. 4

   Inspect the NOx sensor wiring harness and 5-pin connector for melting, corrosion, or physical damage

5. 5

   Monitor live NOx sensor data with a diagnostic scanner to check for erratic readings or flatlining (confirming a dead sensor)

1. 1

   Drain and flush DEF tank

   If the DEF fluid is contaminated or the injector is clogged, drain/flush the tank and replace the DEF filter.

2. 2

   Cool down exhaust system

   Ensure the tractor has been turned off and the exhaust system has completely cooled down, as the sensor operates in an extreme heat environment.

3. 3

   Disconnect NOx sensor

   Locate the faulty NOx sensor on the exhaust pipe (post-catalyst) and carefully unplug its 5-pin connector from the wiring harness.

4. 4

   Remove old sensor

   Unscrew the old NOx sensor from the exhaust pipe.

5. 5

   Prep the new sensor

   Apply a high-temperature anti-seize compound to the threads of the new sensor to prevent it from seizing in the future (ensure no compound gets on the sensor probe itself).

6. 6

   Install new sensor

   Thread the new sensor into the exhaust pipe (M20 x 1.5 thread) and tighten securely.

7. 7

   Reconnect sensor

   Plug the sensor's cable back into the tractor's wiring harness.

8. 8

   Reset SCR system

   Connect a diagnostic tool to the tractor's OBD port to clear the stored 521026.31 fault code and reset the SCR system.